CS_BASICS

pic_source

Resource

Resource.md - Resource for coding interview (keep updating)
ref.md - Leetcode ref
teach yourself CS
MindMapCodeInterview - Mind map for coding interview
CodeInterviewCheatsheet - Coding interview cheetsheet
repl.it - Coding online!
Visualization
- visualgo - DFS / BFS - DFS, BFS visualization
- visualgo - linkedlist - Linkedlist visualization
- visualgo - BST - binary search tree visualization
- toptal-sorting-algorithms- sorting algorithms online
How to: Work at Google — Example Coding/Engineering Interview
bit_manipulation.md - Bit Manipulation Cheet Sheet
Py TimeComplexity - Py basic data structure Time Complexity ref
Py data model - Python data model doc
pgexercises - Postgre exercises
sqlservertutorial
Books
freecodecamp - data-structures
LC interview-experience
Cheatsheet
Data structure
- py core data structure interview
LC Pattern
- LC pattern @ blind : Curated-List-of-Top-100-LeetCode-Questions-to-Save-Your-Time
- Blind Curated 75
- LC top 100 likes
- LC Algorithm Problem Classification
- fucking-algorithm
- fucking-algorithm website
- cheatsheet-leetcode-a4
- 14-patterns-to-ace-any-coding-interview-question
- grokking-the-coding-interview
LC problems
- LC sql high frequent
LC flow
- high level idea : data structure, algorithm
- offer time & space complexity
- code implementation
- offer test case (consider edge case)
- discussion & follow up
System design
- Video
  - Tech Dummies Narendra L Utube
  - nfoQ Utube
- Blog
- Repo
  - system-design-primer repo
SQL
- SQL exercises - w3resource SQL exercises
- SQL tutorial - mode.com sql tutorial
- SQL zoo - SQL test
- 10 SQL Tricks : 10 SQL Tricks That You Didn’t Think Were Possible
- Zachary Thomas' SQL Questions -- The Best Medium-Hard Data Analyst SQL Interview Questions
  - pdf
- Select * SQL
- LinkedIn Learning
- Window Functions
- HackerRank
- W3 Schools
- CodeAcademy
- SQL Bolt
- self-joins-calculate-retention-churn-and-reactivation-metrics
- Prod metric design
Tools
- https://coderpad.io/
- https://codeshare.io/
- http://sqlfiddle.com/

Algorithms content

Database

Shell

Shell Script

Progress

Data Structure

Title	Solution	Use case	Comment	Status
Queue	Python , JS			AGAIN*
Stack	Python , JS stack (via linkedlist), JS - stack (via array)			OK
LinkedList	Python, JS			OK**
Doubly LinkedList	Python, JS			AGAIN
Tree	Python			AGAIN**
Trie	Python			AGAIN
Heap	Python , Java			AGAIN
Max Heap	Python			AGAIN
Array	Python			AGAIN*
Graph	Python , JS. Java-graph, Java-graph-client			OK***
Binary search Tree (BST)	Python, JS, Scala, Java			AGAIN
Hash table	Python, JS	usually for improving `time complexity B(O)` via extra space complexity (time-space tradeoff)	`good basic`	AGAIN****
DirectedEdge	Java			AGAIN

Algorithm

Title	Solution	Use case	Comment	Status
Binary search	Python			AGAIN
Linear search	Python			AGAIN
Breadth-first search (BFS)	Python, JS	`FIND SHORTEST PATH`		AGAIN***
Depth-first search (DFS)	Python, JS	`TO CHECK IF SOMETHING EXIST`	`inorder`, `postorder`, `postorder (can recreate a tree)`	AGAIN***
Bubble sort	Python, JS , C			OK* (3)
Insertion sort	Python, JS	`stable` sort	work very fast for `nearly sorted` array	AGAIN
Bucket sort	Python			AGAIN
Quick sort	Python			AGAIN***
Heap sort	Python			AGAIN**
Merge sort	Python, JS, Java, SQL			OK* (2)
Pancake sort	Python			AGAIN
Selection sort	Python, JS			AGAIN
Topological sort	Python		Topological Sort is a algorithm can find "ordering" on an "order dependency" graph	AGAIN
md5	Python			AGAIN
Union Find	Python 1, Python 2, Java 1			AGAIN
Dynamic programming	JS 1, fibonacci_dp JS			AGAIN
Dijkstra	Python,Java			AGAIN***
Floyd-Warshall	Python			not start
Bellman-Ford	Python			not start
Quick Find	Python, Java	init : O(N), union : O(N), find : O(1)	simple, but slow	AGAIN
Quick Union	Java	init : O(N), union : O(N), find : O(N)	lazy approach, route compression, optimized Quick Find	AGAIN
Quick Union (Improvements)		lazy approach, path compression	AGAIN
Priority Queue (`unsorted`)	Java		AGAIN
LRU cache	Python		LC 146	AGAIN
LFU Cache	Python		LC 460	AGAIN

Array

#	Title	Solution	Time	Space	Difficulty	Note	Status
015	3 Sum	Python	O(n^2)	O(1)	Medium	Curated Top 75, good basic, check with `# 001 Two Sum`, `#018 4 sum`, `Two Pointers`, `good basic`,`amazon`,`fb`	OK******* (7)
016	3 Sum Closest	Python	O(n^2)	O(1)	Medium	`Two Pointers`, `basic`, `good trick`,`3 sum`,google, fb, apple, m$, GS, amazon	AGAIN**** (2)
018	4 Sum	Python	O(n^3)	O(1)	Medium	`k sum`, `Two Pointers`, check `#016 3 sum`, `# 454 4 SUM II`,good trick, `fb`	AGAIN******** (4)
026	Remove Duplicates from Sorted Array	Python, Scala	O(n)	O(1)	Easy	`Two Pointers`, `basic`, `good trick`,`M$` ,`fb`	AGAIN*********** (9)
027	Remove Element	Python, Scala	O(n)	O(1)	Easy	`basic`, `amazon`	OK* (2)
031	Next Permutation	Python, Scala	O(n)	O(1)	Medium	good trick, check, 2 pointers, Uber, GS, `google`,`amazon`, `fb`	AGAIN****************** (8) (MUST)
041	First Missing Positive	Python	O(n)	O(1)	Hard	good trick, hash key , array, LC top 100 like, `amazon`, `fb`, google, apple, uber	AGAIN******** (2)
048	Rotate Image	Python	O(n^2)	O(1)	Medium	Curated Top 75, `basic`, `i,j->j,i` `transpose matrix`, garena, `amazon`, `apple`	AGAIN************* (5) (MUST)
054	Spiral Matrix	Python	O(m n)*	O(1)	Medium	Curated Top 75, good basic, array boundary, matrix,`amazon`	AGAIN**** (4)
057	Insert Interval	Python			Medium	Curated Top 75, good basic, `056 Merge Intervals`	AGAIN********** (4) (MUST!)
059	Spiral Matrix II	Python	O(n^2)	O(1)	Medium	check `# 054 Spiral Matrix`, `amazon`	AGAIN** (2)
066	Plus One	Python	O(n)	O(1)	Easy	`basic`, `digit`, `google`	OK** (2)
073	Set Matrix Zeroes	Python	O(m n)*	O(1)	Medium	Curated Top 75, `matrix`, `amazon`	OK* (4)
080	Remove Duplicates from Sorted Array II	Python	O(n)	O(1)	Medium	`two pointers`,AGAIN, `basic`, `trick`, `fb`, `#26 Remove Duplicates from Sorted Array`	AGAIN************ (8)
118	Pascal's Triangle	Python	O(n^2)	O(1)	Easy	`trick`, `basic`	AGAIN** (2)
119	Pascal's Triangle II	Python	O(n^2)	O(1)	Easy	array, check with `# 118 Pascal's Triangle`, `amazon`	OK** (4)
121	Best Time to Buy and Sell Stock	Python	O(n)	O(1)	Easy	Curated Top 75, `dp`,`basic`,`greedy`,`UBER`, `M$`, `amazon`, `fb`	OK****** (6) (but again)
157	Read N Characters Given Read4	Python	O(n)	O(1)	Easy	🔒, buffer, `google`, `amazon`, `fb`	AGAIN**** (3)
163	Missing Ranges	Python	O(n)	O(1)	Medium	two pointer, 🔒, `google`, `amazon`	AGAIN******* (3)
169	Majority Element	Python	O(n)	O(1)	Easy	`amazon`	OK*
189	Rotate Array	Python	O(n)	O(1)	Medium	array, k % len(nums), good basic, `amazon`	OK* (7) (but again)
209	Minimum Size Subarray Sum	Python	O(n)	O(1)	Medium	good basic, sliding window, `Binary Search`, `trick`,`2 pointers`, `fb`	OK********** (5) (but again)
215	Kth Largest Element in an Array	Python	O(n) ~ O(n^2)	O(1)	Medium	EPI, `quick sort`, bubble sort, sort, `amazon`,`fb`	OK* (2)
228	Summary Ranges	Python	O(n)	O(1)	Easy	check `# 163 Missing Ranges`, `basic`, array, `google`	OK*** (3)
229	Majority Element II	Python	O(n)	O(1)	Medium		OK
238	Product of Array Except Self	Python	O(n)	O(1)	Medium	Curated Top 75, array, LintCode, `good trick`, `Apple`, `M$`, `amazon`, `fb`	OK******* (but again)(5)
240	Search a 2D Matrix II	Python	O(m + n)	O(1)	Medium	LintCode, `basic`, `matrix`, `trick`, `binary search`, check `# 74 Search a 2D Matrix`, `amazon`, `apple`	OK***** (6) (but again)
243	Shortest Word Distance	Python	O(n)	O(1)	Easy	🔒, `basic`	OK*
245	Shortest Word Distance III	Python	O(n)	O(1)	Medium	🔒, check `Shortest Word Distance I II III`	OK*
251	Flatten 2D Vector	Python	O(1)	O(1)	Medium	🔒, `good basic`, check`# 341 Flatten Nested List Iterator`, `google`, `airbnb`, `twitter`, `amazon`	AGAIN******** (4)
277	Find the Celebrity	Python	O(n)	O(1)	Medium	graph, 🔒, `fb`,`amazon`, `trick`	AGAIN********** (5)
287	Find the Duplicate Number	Python			Medium	good trick,binary search, cycle linked list, check `# 142 Linked List Cycle II`, `amazon`	OK* (2)
289	Game of Life	Python	O(m n)*	O(1)	Medium	simultaneous,matrix,`complex`, `google`, `amazon`	AGAIN*** (4)
293	Flip Game	Python	O(n (c+1))*	O(1)	Easy	🔒, `basic`	AGAIN*
308	Range Sum Query 2D - Mutable	Python	O(n (c+1))*	O(1)	Hard	LC 303, pre-sum, matrix, tree, 🔒, `google`	not start
311	Sparse Matrix Multiplication	Python	O(m n * l)*	O(m l)*	Medium	🔒, matrix, `basic`, `fb`	OK**** (4)
334	Increasing Triplet Subsequence	Python	O(n)	O(1)	Medium	AGAIN, check `# 300 Longest Increasing Subsequence`, `trick`, `fb`, variables	OK***** (but again) (4)
370	Range Addition	Python	O(k + n)	O(1)	Medium	prefix sum, array, 🔒, check `# 598 Range Addition II`, `amazon`	AGAIN************** (4) (MUST)
384	Shuffle an Array	Python	O(n)	O(n)	Medium	EPI, `trick`	OK*
396	Rotate Function	Python	O(n)	O(1)	Medium	can pass, math, `trick`, `amazon`	AGAIN*** (3)
412	Fizz Buzz	Python, Scala	O(n)	O(1)	Easy		OK
414	Third Maximum Number	Python	O(n)	O(1)	Easy	`good basic`, `amazon`	OK* (4)
419	Battleships in a Board	Python	O(m n)*	O(1)	Medium		AGAIN*
422	Valid Word Square	Python	O(m n)*	O(1)	Easy	🔒, `basic`, `matrix`	AGAIN*
442	Find All Duplicates in an Array	Python	O(n)	O(1)	Medium		OK*
448	Find All Numbers Disappeared in an Array	Python	O(n)	O(1)	Easy		OK
498	Diagonal Traverse	Python	O(n)	O(1)	Medium	`matrix`,`google`,`fb`	AGAIN*** (3) (not start)
531	Lonely Pixel I	Python	O(m n)*	O(m + n)	Medium	🔒, `matrix`, `basic`	AGAIN*
533	Lonely Pixel II	Python	O(m n)*	O(m n)*	Medium	🔒	AGAIN (not start*)
565	Array Nesting	Python	O(n)	O(1)	Medium	`union find`,`dfs`,`apple`	AGAIN**** (1)
566	Reshape the Matrix	Python	O(m n)*	O(m n)*	Easy	`basic`, `matrix`	AGAIN**
581	Shortest Unsorted Continuous Subarray	Python	O(n)	O(1)	Easy	`basic`	AGAIN*
605	Can Place Flowers	Python	O(n)	O(1)	Easy	`pass vs continue`	OK*
624	Maximum Distance in Arrays	Python	O(n)	O(1)	Easy	🔒	AGAIN*
643	Maximum Average Subarray I	Python	O(n)	O(1)	Easy	`Math`, `basic`	AGAIN*
661	Image Smoother	Python	O(m n)*	O(1)	Easy	`matrix`,`basic`, `amazon`	OK***** (4) (but again!)
665	Non-decreasing Array	Python	O(n)	O(1)	Easy		AGAIN (not start)
667	Beautiful Arrangement II	Python	O(n)	O(1)	Medium		AGAIN (not start)
670	Maximum Swap	Python	O(logn)	O(logn)	Medium	`good basic`, reversed, str -> list,string + pointers , `fb`	AGAIN************ (9) (MUST)
674	Longest Continuous Increasing Subsequence	Python	O(n)	O(1)	Easy	`good basic`,`dp`,`2 pointers` ,`array` ,`fb`	OK*** (5)
697	Degree of an Array	Python	O(n)	O(n)	Easy		AGAIN (not start)
713	Subarray Product Less Than K	Python	O(n)	O(1)	Medium	`basic`, `sliding window`, good trick	OK****** (3) (but again)
717	1-bit and 2-bit Characters	Python	O(n)	O(1)	Easy	Greedy	AGAIN (not start)
723	Candy Crush	Python	O((R C)^2)*	O(1)	Medium	`complex`	AGAIN (not start)
724	Find Pivot Index	Python	O(n)	O(1)	Easy		OK*
729	My Calendar I	Python	O(nlogn)	O(n)	Medium	`python class`	AGAIN* (not start)
731	My Calendar II	Python	O(n^2)	O(n)	Medium	`trick`, `basic`	AGAIN** (not start)
747	Largest Number At Least Twice of Others	Python	O(n)	O(1)	Easy	`good basic`, `data structure`	OK*
755	Pour Water	Python	O(v n)*	O(1)	Medium	`complex`	AGAIN (not start)
766	Toeplitz Matrix	Python	O(m n)*	O(1)	Easy	`basic`, `matrix`, `google`	AGAIN* (2)
769	Max Chunks To Make Sorted	Python	O(n)	O(1)	Medium		AGAIN** (not start)
792	Number of Matching Subsequences	Python	O(n + w)	O(1)	Medium	`trick`	AGAIN* (not start)
794	Valid Tic-Tac-Toe State	Python	O(1)	O(1)	Medium	`complex`	AGAIN
795	Number of Subarrays with Bounded Maximum	Python	O(n)	O(1)	Medium		AGAIN (not start*)
807	Max Increase to Keep City Skyline	Python	O(n^2)	O(n)	Medium		AGAIN*
821	Shortest Distance to a Character	Python	O(n)	O(1)	Easy	`basic`, `trick`	AGAIN**
830	Positions of Large Groups	Python	O(n)	O(1)	Easy	`basic`	AGAIN*
832	Flipping an Image	Python	O(n^2)	O(1)	Easy		AGAIN*
835	Image Overlap	Python	O(n^4)	O(n^2)	Medium		AGAIN (not start)
840	Magic Squares In Grid	Python	O(m n)*	O(1)	Easy	`complex`	AGAIN (not start)
842	Split Array into Fibonacci Sequence	Python	O(n^3)	O(n)	Medium	check `# 306 Addictive Number`, `basic`, `dfs`, `fibonacci`	AGAIN* (not start)
845	Longest Mountain in Array	Python	O(n)	O(1)	Medium	`basic`, `trick`	AGAIN* (not start)
849	Maximize Distance to Closest Person	Python	O(n)	O(1)	Easy	`basic`, `trick`	AGAIN (not start*)
860	Lemonade Change	Python	O(n)	O(1)	Easy	amazon	OK* (2)
0868	Transpose Matrix	Python	O(r c)*	O(1)	Easy	`basic`	OK*
885	Spiral Matrix III	Python	O(max(m, n)^2)	O(1)	Medium	`basic`	AGAIN* (not start)
888	Fair Candy Swap	Python	O(m + n)	O(m + n)	Easy	`basic`, `trick`	OK*
896	Monotonic Array	Python	O(n)	O(1)	Easy	`all`,`array` ,`fb`	OK
905	Sort Array By Parity	Python	O(n)	O(1)	Easy	`sort by lambda`	OK
909	Snakes and Ladders	Python	O(n^2)	O(n^2)	Medium	array, matrix, dfs,`complex`, `amazon`	AGAIN***** (3)
915	Partition Array into Disjoint Intervals	Python	O(n)	O(n)	Medium	`basic`, `trick`	AGAIN* (not start)
918	Maximum Sum Circular Subarray	Python	O(n)	O(1)	Medium	check `# 053 Maximum Subarray`, `basic`, `trick`	AGAIN* (not start)
921	Minimum Add to Make Parentheses Valid	Python	O(n)	O(1)	Medium	`basic`, `trick`	AGAIN**
922	Sort Array By Parity II	Python	O(n)	O(1)	Easy	`basic`	AGAIN*
923	3Sum With Multiplicity	Python	O(n^2)	O(n)	Medium		AGAIN (not start)
932	Beautiful Array	Python	O(n)	O(n)	Medium	`basic`, `trick`	AGAIN (not start)
941	Valid Mountain Array	Python	O(n)	O(1)	Easy	`basic`, `good basic`	AGAIN*
945	Minimum Increment to Make Array Unique	Python	O(nlogn)	O(n)	Medium	`trick`, `good`	AGAIN**
947	Most Stones Removed with Same Row or Column	Python	O(n)	O(n)	Medium	Union Find , `trick`	AGAIN (not start)
949	Largest Time for Given Digits	Python	O(1)	O(1)	Easy		OK*
950	Reveal Cards In Increasing Order	Python	O(n)	O(n)	Medium		AGAIN (not start)
954	Array of Doubled Pairs	Python	O(n + klogk)	O(k)	Medium	`counter`, `dict`, `trick`	AGAIN**
961	N-Repeated Element in Size 2N Array	Python	O(n)	O(1)	Easy		OK
989	Add to Array-Form of Integer	Python	O(n)	O(1)	Easy	add xxx to sum, fb	AGAIN (not start)
004	Median of Two Sorted Arrays	Python	O(n)	O(1)	Hard	array, heapq, binary search, amazon	AGAIN* (1)
010	Regular Expression Matching	Python	O(n)	O(1)	Hard	recursion, dp, `fb`	AGAIN (not start)
056	Merge Intervals	Python	O(n)	O(1)	Medium	Curated Top 75, `good trick`,057 Insert Interval, `twitter`,`M$`,`UBER`,`google`,`amazon`,`fb`	OK********* (6) (but AGAIN)
759	Employee Free Time	Python	O(n)	O(1)	Hard	LC 56 and LC 986, heap, merger intervals, scanning line, `amazon`, fb, google, uber, airbnb	AGAIN********** (2) (not start)
1014	Best Sightseeing Pair	Python			Medium	dp, array, good basic, Spotify	AGAIN (not start)
1027	Longest Arithmetic Subsequence	Python			Medium	dp, hash table, trick, google, amazon	AGAIN*** (not start)
1041	Robot Bounded In Circle	Python			Medium	array, math, `amazon`	AGAIN** (2)
1109	Corporate Flight Bookings	Python			Medium	array, `amazon`	AGAIN (not start)
1248	Count Number of Nice Subarrays	Python			Medium	LC 828, hash map, Prefix sum, dict, windown, good basic, deque, array, `amazon`	AGAIN************** (3) (MUST)
1275	Find Winner on a Tic Tac Toe Game	Python			Easy	`amazon`	AGAIN (not start)
1567	Maximum Length of Subarray With Positive Product	Python			Medium	good trick, array, dp, 2 pointers, amazon	AGAIN**** (1) (not start)
1914	Cyclically Rotating a Grid	Python			Medium	array, brute force, dequeue`amazon`	AGAIN (not start)

Hash Table

#	Title	Solution	Time	Space	Difficulty	Status	Note
001	Two Sum	Python, Java,Scala	O(n)	O(n)	Easy	`good basic`, `hash table`, `apple`, `amazon`, `UBER`, `grab`, `fb`	OK*** (6) (but again)
003	Longest Substring Without Repeating Characters	Python	O(n)	O(1)	Medium	Curated Top 75, 2 pointers, optimized (SLIDING WINDOW + DICT),`good trick`, `hashMap`, sliding window, `apple`,`amazon`,`fb`	AGAIN**************** (9) (but AGAIN)
036	Valid Sudoku	Python	O(9^2)	O(9)	Medium	`UBER`, `apple`, `amazon`	OK** (2) (again)
049	Group Anagrams	Python, Scala	O(n glogg)*	O(n)	Medium	Curated Top 75, `good basic`, dict,`trick`,`dict + sort`, `UBER`, `amazon`, `fb`	OK ********** (6)
170	Two Sum III - Data structure design	Python	O(n)	O(n)	Easy	🔒, `trick`,`good basic`, `linkedin`, `fb`	OK*** (4)
187	Repeated DNA Sequences	Python	O(n)	O(n)	Medium	`basic`,`trick`,`set`, `linkedin`	AGAIN**
202	Happy Number	Python	O(k)	O(k)	Easy	`twitter`,`airbnb`, `UBER`	AGAIN** (3)
204	Count Primes	Python	O(n)	O(n)	Medium	`good trick`, cache, dict, set, `M$`, `amazon`	AGAIN******** (5)
205	Isomorphic Strings	Python	O(n)	O(1)	Easy	`basic`, `trick`, `bloomberg`	AGAIN**
217	Contains Duplicate	Python	O(n)	O(n)	Easy	Curated Top 75, `yahoo`, `airbnb`	OK
219	Contains Duplicate II	Python	O(n)	O(n)	Easy	`basic`, `trick`, `hash table`	AGAIN*
244	Shortest Word Distance II	Python	ctor: O(n), lookup: O(a + b)	O(n)	Medium	🔒	AGAIN (not start*)
246	Strobogrammatic Number	Python	O(n)	O(1)	Easy	🔒, `google`, `fb`	OK* (4)
249	Group Shifted Strings	Python	O(nlogn)	O(n)	Easy	🔒,`apple`, `UBER`, `google`	AGAIN* (4) (not start)
266	Palindrome Permutation	Python	O(n)	O(1)	Easy	🔒	OK
288	Unique Word Abbreviation	Python	ctor: O(n), lookup: O(1)	O(k)	Medium	🔒, ?, google	AGAIN (2)(not start)
290	Word Pattern	Python	O(n)	O(c)	Easy	`basic`, chcek `# 205 Isomorphic Strings`,`good basic`, `for ptn, word in zip(pattern, words)`, `dropbox` , `UBER`	AGAIN* (3)
299	Bulls and Cows	Python	O(n)	O(1)	Easy	`trick`,`map(operator.eq, a, b)`,`amazon`, `airbnb`, `google`	AGAIN* (3)
314	Binary Tree Vertical Order Traversal	Python	O(n)	O(n)	Medium	🔒, `BFS`,`DFS`,`hash table`, `tree`, `trick`,`google`, `amazon`,`fb`, m$	OK**** (6)
325	Maximum Size Subarray Sum Equals k	Python	O(n)	O(n)	Medium	prefix sum, 🔒, `basic`, `good trick`, `dict`, `fb`	AGAIN************ (7) (MUST)
356	Line Reflection	Python	O(n)	O(n)	Medium	🔒, Hash, Two Pointers,`math`,`google`	AGAIN (not start)
387	First Unique Character in a String	Python	O(n)	O(n)	Easy	`amazon`, `apple`, `fb`	OK
388	Longest Absolute File Path	Python	O(n)	O(d)	Medium	stack, hash table, good trick, file system, `google`	AGAIN******* (3)
409	Longest Palindrome	Python	O(n)	O(1)	Easy		OK*
424	Longest Repeating Character Replacement	Python	O(n)	O(1)	Medium	Curated Top 75, `silding window`, `two pointers`, `good trick`, LC blind pattern	AGAIN********* (6)
438	Find All Anagrams in a String	Python	O(n)	O(1)	Medium	`trick`, `AGAIN`, `sliding window`,`acc Counter`,`amazon`,`fb`, apple, google, uber, yahoo	AGAIN************** (8)
447	Number of Boomerangs	Python	O(n^2)	O(n)	Easy	`trick`, `google`	AGAIN (3) (not start)
454	4Sum II	Python	O(n^2)	O(n^2)	Medium	check LC 018 4SUM, `trick`, `basic`, `amazon`	AGAIN**
463	Island Perimeter	Python	O(n)	O(k)	Medium	`basic`,`hash table`, `google`, `fb`, amazon	AGAIN** (2)
470	Implement Rand10() Using Rand7()	Python	O(1)	O(1)	Medium	`trick`, `google`	AGAIN** (3)
473	Matchsticks to Square	Python	O(n s * 2^n)*	O(n (2^n + s))*	Medium	`complex`,`hard`	AGAIN (not start)
523	Continuous Subarray Sum	Python	O(n)	O(k)	Medium	sub array sum, check `# 560 Subarray Sum Equals K`,`good trick`,`substring`, `hash table`,`AGAIN`,`M$`,`fb`, `apple`	AGAIN*************** (10) (MUST)
525	Contiguous Array	python	O(n)	O(n)	Medium	sub-array sum, `good basic`, `array`, `hashmap`, `cache`, `AGAIN`, `fb`, amazon	AGAIN*************** (11) (MUST)
532	K-diff Pairs in an Array	Python	O(n)	O(n)	Medium	hash table, `basic`, `collections.Counter()`,`a-b =k -> a = k + b` , `amazon`	AGAIN********** (6)
554	Brick Wall	Python	O(n)	O(m)	Medium	`trick`,`hash map`, `bloomberg`, `fb`, grab	AGAIN******** (5)
560	Subarray Sum Equals K	Python	O(n)	O(n)	Medium	`must check`,check `# 523 Continuous Subarray Sum`, LC 1268,`basic`, `substring`,`good trick`,`google`,`fb`	AGAIN************** (6) (MUST)
561	Array Partition I	Python	O(r)	O(r)	Easy		OK
575	Distribute Candies	Python	O(n)	O(n)	Easy		OK
594	Longest Harmonious Subsequence	Python	O(n)	O(n)	Easy	`basic`, `good trick`	OK* (3)
599	Minimum Index Sum of Two Lists	Python	O((m + n) l)*	O(m l)*	Easy	`yelp`	OK*
609	Find Duplicate File in System	Python	O(n l)*	O(n l)*	Medium	`collections.defaultdict(list)`, `dropbox`	OK*
657	Robot Return to Origin	Python			Easy	`amazon`	OK (2)
748	Shortest Completing Word	Python	O(n)	O(1)	Easy	`collections.Counter`, `hash table`,`google`	AGAIN* (3)
760	Find Anagram Mappings	Python	O(n)	O(n)	Easy	`basic`, `collections.defaultdict`	OK
771	Jewels and Stones	Python	O(m + n)	O(n)	Easy	`amazon`	OK (2)
811	Subdomain Visit Count	Python	O(n)	O(n)	Easy	`indeed`, `bloomberg`	AGAIN (not start)
822	Card Flipping Game	Python	O(n)	O(n)	Medium	`good basic`	AGAIN* (3)
825	Friends Of Appropriate Ages	Python	O(a^2 + n)	O(a)	Medium	`good basic`,`counter`,`AGAIN`,`fb`	AGAIN***** (5)
869	Reordered Power of 2	Python	O(1)	O(1)	Medium	`trick`,`basic`, `bit manipulation`, `bit`	AGAIN*
873	Length of Longest Fibonacci Subsequence	Python	O(n^2)	O(n)	Medium	`trick`, `DP`, `Fibonacci`, `set`	AGAIN**
957	Prison Cells After N Days	Python	O(1)	O(1)	Medium	`trick`, `DP`, `mod`	AGAIN (not start)
966	Vowel Spellchecker	Python	O(n)	O(w)	Medium	`trick`, `dict`, `set`	AGAIN (not start)
974	Subarray Sums Divisible by K	Python	O(n)	O(k)	Medium	variant of `# 560 Subarray Sum Equals K` , `trick`, `basic`	AGAIN** (3) (not start)
992	Subarrays with K Different Integers	Python	O(n)	O(k)	Hard	2 pointers, hashmap, sliding window, amazon	AGAIN (not start)
1010	Pairs of Songs With Total Durations Divisible by 60	Python			Medium	good basicm dict, array, `amazon`	AGAIN********* (4) (MUST)
1099	Two Sum Less Than K	Python			Medium	dict, sort, `amazon`	AGAIN* (1) (not start)
1131	Rank Transform of an Array	Python			Easy	dict, array, `amazon`	OK* (1)
1296	Divide Array in Sets of K Consecutive Numbers	Python			Medium	LC 846, dict, `google`	AGAIN (not start)
1923	Longest Common Subpath	python	O(n)	O(h)	Hard	hash, bit, `amazon`	AGAIN (not start)

Linked list

#	Title	Solution	Time	Space	Difficulty	Note	Status
002	Add Two Numbers	Python	O(n)	O(1)	Medium	Curated Top 75, check `# 445 Add Two Numbers II`, `basic`, `linked list`, `airbnb`, `amazon`, `fb`	OK**** (5) (but again)
021	Merge Two Sorted Lists	Python	O(n)	O(1)	Easy	Curated Top 75, `UBER`, `amazon`, `apple`, `fb`	OK******** (6) (but again)
023	Merge k sorted lists	python	O(n)	O(h)	Hard	Curated Top 75, linked list, check `#21 Merge Two Sorted Lists`, `amazon`	OK**** (2) (but again !!!
024	Swap Nodes in Pairs	Python	O(n)	O(1)	Easy	`GOOD basic`, LC 100 like, `UBER`,`amazon`, `fb`	AGAIN************* (5) (MUST)
025	Reverse Nodes in k-Group	Python	O(n)	O(1)	Hard	good trick, reverse linkedlist, reverse K linkedlist, amazon, google, fb, m$	AGAIN********** (4)
061	Rotate List	Python	O(n)	O(1)	Medium	`basic`	AGAIN (2)
082	Remove Duplicates from Sorted List II	Python	O(n)	O(1)	Medium	check `# 083 Remove Duplicates from Sorted List`	AGAIN (2)
083	Remove Duplicates from Sorted List	Python	O(n)	O(1)	Easy	`basic`	OK*
092	Reverse Linked List II	Python	O(n)	O(1)	Medium	`# 206 Reverse Linked List`, `good trick`, fb, apple, google, amazon, m$	AGAIN*********** (5 (MUST)
138	Copy List with Random Pointer	Python	O(n)	O(1)	Medium	trick, linked list,`hash table`,`UBER`, `M$`, `amazon`, `fb`	AGAIN***** (6)
160	Intersection of Two Linked Lists	Python	O(m + n)	O(1)	Easy	basic, `airbnb`, `amazon`,`fb`	OK******* (6) (again!)
203	Remove Linked List Elements	Python	O(n)	O(1)	Easy	linked list basic,`amazon`	AGAIN** (2)
206	Reverse Linked List	Python	O(n)	O(1)	Easy	Curated Top 75, `good basic`,`amazon`,`fb`	OK*********** (9) (MUST again)
234	Palindrome Linked List	Python	O(n)	O(1)	Easy	linked list,`amazon`,`fb`	OK (4)
237	Delete Node in a Linked List	Python	O(1)	O(1)	Easy	LintCode, apple	OK * (1) (but again)
328	Odd Even Linked List	Python	O(n)	O(1)	Medium	`basic`	OK** (2)
369	Plus One Linked List	Python	O(n)	O(1)	Medium	🔒, `basic`, `trick`	AGAIN* (2)
445	Add Two Numbers II	Python	O(m + n)	O(m + n)	Medium	`trick`, linked list, string,`good basic`, `amazon`	AGAIN*** (3)
725	Split Linked List in Parts	Python	O(n + k)	O(1)	Medium	mod, split linked list, linked list, good trick,`amazon`	AGAIN************ (6) (again)
817	Linked List Components	Python	O(m + n)	O(m)	Medium		OK*
430	Flatten a Multilevel Doubly Linked List	Python			Medium	`good trick`,`doubly linked list`,`AGAIN`,`dfs`, `fb`	AGAIN********* (4)
708	Insert into a Cyclic Sorted List	python	O(n)	O(h)	Medium	`AGAIN`,`cyclic linked list`,`good trick`, `google`, `amazon`, `fb`	AGAIN******** (4)

Stack

#	Title	Solution	Time	Space	Difficulty	Note	Status
020	Valid Parentheses	Python	O(n)	O(n)	Easy	Curated Top 75, `good basic`,`fb`, `amazon`	OK** (6)
032	Longest Valid Parentheses	Python	O(n)	O(n)	Hard	brute force, dp, stackm deque, LC top 100 likes, `amazon`, fb, m$	AGAIN***** (1) (not start)
071	Simplify Path	Python	O(n)	O(n)	Medium	`basic`, `stack`, `amazon`,`fb`	OK** (5)
085	Maximal Rectangle	Python	O(n)	O(n)	Hard	top-100-like, brute force, stack, dp, LC 084, google, amazon, apple	AGAIN (not start)
101	Symmetric Tree	Python	O(n)	O(h)	Easy	`good basic`,`bfs`, `dfs`, `linkedin`, `M$`,`amazon`, `fb`, google	AGAIN********** (4)
150	Evaluate Reverse Polish Notation	Python	O(n)	O(n)	Medium	stack, good trick,`amazon`	AGAIN******* (4)
155	Min Stack	Python	O(n)	O(1)	Easy	basic, stack, data structure, `amazon`	OK******* (4)
173	Binary Search Tree Iterator	python	O(1)	O(h)	Medium	`good basic`,`tree, stack, M$`, `linkedin`, `google`,`amazon`,`fb`	OK***** (5)
224	Basic Calculator	python	O(n)	O(n)	Hard	`basic`,`trick`,`stack`, LC 227, amazon	AGAIN******* (3)
227	Basic Calculator II	python	O(n)	O(n)	Medium	delay op, LC 224, `good trick`,`stack`,`airbnb` ,`fb`, amazon	AGAIN************** (6) (MUST)
232	Implement Queue using Stacks	python	O(1), amortized	O(n)	Easy	stack, stack-queue, EPI, LintCode, `amazon`	OK** (2)
255	Verify Preorder Sequence in Binary Search Tree	python	O(n)	O(1)	Medium	🔒	AGAIN (not start)
331	Verify Preorder Serialization of a Binary Tree	python	O(n)	O(1)	Medium		AGAIN (not start)
341	Flatten Nested List Iterator	python	O(n)	O(h)	Medium	LC 284, 🔒 Iterator, stack, generator, `good basic`,`amazon`,`fb***`	AGAIN********* (6)
385	Mini Parser	python	O(n)	O(h)	Medium		AGAIN
394	Decode String	python	O(n)	O(h)	Medium	stack, good basic!!!!, pre num string, LC 224, LC 227, `amazon`, `google`	AGAIN************** (6) (MUST)
439	Ternary Expression Parser	python	O(n)	O(1)	Medium	🔒	AGAIN (not start)
456	132 Pattern	python	O(n)	O(n)	Medium		AGAIN (not start)
496	Next Greater Element I	python	O(n)	O(n)	Easy	good basic, stack, LC 739, LC 503, LC 406	OK****** (3) (but again)
503	Next Greater Element II	python	O(n)	O(n)	Medium	good basic, stack, LC 739, LC 503, LC 406	AGAIN************* (7)
636	Exclusive Time of Functions	python	O(n)	O(n)	Medium	`trick`,`AGAIN`,`stack`,`UBER`, `fb`	AGAIN********** (4)
682	Baseball Game	python	O(n)	O(n)	Easy	good basic, stack,`amazon`	OK* (3)
735	Asteroid Collision	python	O(n)	O(n)	Medium	good basic, stack, m$, GS, fb, `amazon`	AGAIN************** (5)
739	Daily Temperatures	python	O(n)	O(n)	Medium	LC 739, LC 503, LC 406, AGAIN, stack, good trick,`amazon`	AGAIN******************* (9) (MUST)
772	Basic Calculator III	python	O(n)	O(n)	Medium	check LC 224, 227	AGAIN (not start)
853	Car Fleet	python	O(nlogn)	O(n)	Medium		AGAIN (not start)
856	Score of Parentheses	python	O(n)	O(1)	Medium		AGAIN (not start)
872	Leaf-Similar Trees	python	O(n)	O(h)	Easy		AGAIN*
895	Maximum Frequency Stack	python	O(n)	O(h)	Hard	good basic, heap, design, stack, amazon, apple, linkedin, m$, twitter	AGAIN********** (1) (not start)
901	Online Stock Span	python	O(n)	O(n)	Medium		AGAIN (not start)
946	Validate Stack Sequences	python	O(n)	O(n)	Medium		AGAIN
1047	Remove All Adjacent Duplicates in String	python	O(n)	O(n)	easy	good basic, fb, amazon, google	AGAIN************ (3) (MUST)
1209	Remove All Adjacent Duplicates in String II	python	O(n)	O(n)	Medium	good basic, stack, two pointers, greedy, fb, amamzon, apple, spotify	AGAIN************ (3) (MUST)
1703	Minimum Adjacent Swaps for K Consecutive Ones	python	O(n)	O(n)	Hard	heap, sliding window, amazon	AGAIN (not start)
1896	Minimum Cost to Change the Final Value of Expression	python	O(n)	O(n)	Hard	complex, stack, dp, dp+stack, dfs, `amazon`	AGAIN (not start)

Tree

#	Title	Solution	Time	Space	Difficulty	Note	Status
094	Binary Tree Inorder Traversal	python	O(n)	O(1)	Medium	`good basic`,`Morris Traversal`, `M$`, `fb`	AGAIN**** (3)
124	Binary Tree Maximum Path Sum	python	O(n)	O(1)	Hard	Curated Top 75, google, amazon, fb, m$, twitter	AGAIN******* (2)
144	Binary Tree Preorder Traversal	python	O(n)	O(1)	Medium	`Morris Traversal`	AGAIN
208	Implement Trie (Prefix Tree)	python	O(n)	O(1)	Medium	Curated Top 75, dict tree, trie, `amazon`,`fb`	AGAIN************** (6) (MUST)
211	Add and Search Word - Data structure design	python	O(min(n, h))	O(min(n, h))	Medium	Curated Top 75, `Trie`, `DFS`, do `# 208 first`,`amazon` ,`fb`	AGAIN***** (5)
226	Invert Binary Tree	python	O(n)	O(h), O(w)	Easy	Curated Top 75, good basic	OK******* (4) (but again)
307	Range Sum Query - Mutable	python	ctor: O(n), update: O(logn), query: O(logn)	O(n)	Medium	LintCode, DFS, Segment Tree, BIT, check `#303 Range Sum Query - Immutable`	AGAIN* (2)(not start)
536	Construct Binary Tree from String	python, java	O(n)	O(h)	Medium	🔒, tree, recursive, `trick`, check `# 606 Construct String from Binary Tree`, `amazon`	AGAIN******** (5)
538	Convert BST to Greater Tree	python	O(n)	O(h)	Medium	good basic, dfs, bfs, tree, `amazon`	OK********* (6) (but again!)
543	Diameter of Binary Tree	python	O(n)	O(h)	Easy	`trick`,`google`,`amazon`,`fb`	AGAIN**** (2)
545	Boundary of Binary Tree	python	O(n)	O(h)	Medium	recursive, dfs, tree boundary, tree,🔒, `good trick`, `amazon`	AGAIN********* (6)
548	Split Array with Equal Sum	python	O(n^2)	O(n)	Medium	🔒, `good trick`, `array`	AGAIN*** (2)
563	Binary Tree Tilt	python	O(n)	O(n)	Easy		AGAIN
572	Subtree of Another Tree	python	O(m n)*	O(h)	Easy	Curated Top 75, LC 100, tree,good basic, dfs, bfs	`amazon`,`fb`
606	Construct String from Binary Tree	python	O(n)	O(h)	Easy	good basic, tree, dfs, LC # 536, `amazon`	OK******** (7) (again!)
617	Merge Two Binary Trees	python	O(n)	O(h)	Easy	tree, dfs, bfs, `good basic`, `amazon`	OK******* (4) (but again)
623	Add One Row to Tree	python	O(n)	O(h)	Medium	`good basic`, `dfs`, `bfs`	AGAIN** (2)
637	Average of Levels in Binary Tree	python	O(n)	O(h)	Easy	`bfs`, `dfs`, `good basic`, `fb`	OK* (3)
652	Find Duplicate Subtrees	python	O(n)	O(n)	Medium	AGAIN, good basic,dfs, Hash, `amazon`	AGAIN************** (6)
653	Two Sum IV - Input is a BST	python	O(n)	O(h)	Easy	Two Pointers,`2 sum`,`bfs`, `dfs`,`amazon`,`fb`	OK*** (3)
654	Maximum Binary Tree	python	O(n)	O(n)	Medium	LintCode, Descending Stack, `good basic`	AGAIN* (2)
655	Print Binary Tree	python	O(n)	O(h)	Medium		AGAIN* (2) (not start)
662	Maximum Width of Binary Tree	python	O(n)	O(h)	Medium	width of tree, bfs, dfs, `trick`, `amazon`	AGAIN********* (5)
663	Equal Tree Partition	python	O(n)	O(n)	Medium	`# LC 508`, AGAIN, 🔒 , Hash, tree, dfs ,`trick`, `good trick`, `amazon`	OK******** (8)
677	Map Sum Pairs	python	O(n)	O(t)	Medium	Trie, `trick`, `hard`	AGAIN* (2) (not start)
684	Redundant Connection	python	O(n)	O(n)	Medium	Union Find, `trick`, `basic`	AGAIN** (2) (not start)
687	Longest Univalue Path	python	O(n)	O(h)	Easy	`basic`, dfs, tree, `trick`, `google`	AGAIN** (3)
814	Binary Tree Pruning	python	O(n)	O(h)	Medium	DFS, `basic`	AGAIN* (2)
863	All Nodes Distance K in Binary Tree	python	O(n)	O(n)	Medium	LC 752, tree, DFS + BFS, `trick`, `hard`, `amazon`	AGAIN************ (4)
866	Smallest Subtree with all the Deepest Nodes	python	O(n)	O(h)	Medium	`DFS`, `trick`, `basic`	AGAIN** (2)
889	Construct Binary Tree from Preorder and Postorder Traversal	python	O(n)	O(h)	Medium	`DFS`, `stack`, `trick`	AGAIN** (2) (not start*)
897	Increasing Order Search Tree	python	O(n)	O(h)	Easy	`DFS`, `good basic`,`inorder`	AGAIN** (2)
919	Complete Binary Tree Inserter	python	ctor: O(n) insert: O(1) get_root: O(1)	O(n)	Medium	`bst`	AGAIN** (2)
938	Range Sum of BST	python	O(n)	O(h)	Medium	DFS, check `# 108 Convert Sorted Array to Binary Search Tree`	AGAIN* (2)
951	Flip Equivalent Binary Trees	python	O(n)	O(h)	Medium	DFS	AGAIN* (2)
958	Check Completeness of a Binary Tree	python	O(n)	O(w)	Medium	`BFS`, `DFS`, `basic`	AGAIN** (2)
965	Univalued Binary Tree	python	O(n)	O(h)	Easy	`DFS`, `BFS`, `good basic`	AGAIN** (2)
971	Flip Binary Tree To Match Preorder Traversal	python	O(n)	O(h)	Medium	DFS, `trick`	AGAIN** (2) (not start)
979	Distribute Coins in Binary Tree	python	O(n)	O(h)	Medium	DFS, `trick`	AGAIN*** (2)
508	Most Frequent Subtree Sum	python			Medium	tree, dfs, bfs, good basic,`amazon`	OK*********** (4) (but again MUST)
297	Serialize and Deserialize Binary Tree	python			Hard	Curated Top 75, tree, binary tree, DFS, check `#449 Serialize and Deserialize BST` ,`amazon`	AGAIN********** (4) (MUST)
683	K Empty Slots	python			Hard	BST, tree, bucket, `google`	not start
701	Insert into a Binary Search Tree	python			Medium	good basic, BST, tree, BFS, DFS	OK*** (2)
1339	Maximum Product of Splitted Binary Tree	python			Medium	dfs, tree, amazon	AGAIN*** (1) (not start)
1372	Longest ZigZag Path in a Binary Tree	python			Medium	dfs, bfs, post order, good trick, tree, amazon	AGAIN*** (1) (not start)

Heap

#	Title	Solution	Time	Space	Difficulty	Note	Status
264	Ugly Number II	python	O(n)	O(1)	Medium	good trick, LC 263, LC 313, Heap, LintCode , DP, M$	AGAIN*********** (4) (MUST)
313	Super Ugly Number	python	O(n k)*	O(n + k)	Medium	BST, Heap	AGAIN (not start*)
373	Find K Pairs with Smallest Sums	python	O(k log(min(n, m, k)))*	O(min(n, m, k))	Medium		AGAIN (not start)
378	Kth Smallest Element in a Sorted Matrix	python	O(k log(min(n, m, k)))*	O(min(n, m, k))	Medium	LintCode	AGAIN (not start)
846	Hand of Straights	python	O(nlogn)	O(n)	Medium	LC 1296, google, hashmap	OK*
855	Exam Room	python	seat: O(logn) leave: O(logn)	O(n)	Medium	BST, Hash, `trick`	AGAIN* (2) (not start)
295	Find Median from Data Stream	python			Hard	Curated Top 75, priority queue, trick ,heap, stream, `amazon`	AGAIN****** (6)
703	Kth Largest Element in a Stream	python			Easy	heap, stream, `amazon`	AGAIN***** (4)
1130	Minimum Cost Tree From Leaf Values	Python			Medium	LC 1167,heap	not start
1167	Minimum Cost to Connect Sticks	Python			Medium	LC 1130, good basic,heap,`amazon`	AGAIN***** (3)
1353	Maximum Number of Events That Can Be Attended	Python			Medium	LC 252, 253, good trick, meeting room, heap, greedy, brute force, PRIORITY QUEUE, dp, bit, fb, twitter, `amazon`	AGAIN********* (2) MUST
1481	Least Number of Unique Integers after K Removals	Python			Medium	good trick, greedy, Counter, dict, heap,`amazon`	AGAIN******** (3)

Bit Manipulation

#	Title	Solution	Time	Space	Difficulty	Note	Status
136	Single Number	Python	O(n)	O(1)	Easy	`airbnb`,`amazon`,`fb`	OK
137	Single Number II	Python	O(n)	O(1)	Medium		OK
190	Reverse Bits	Python	O(1)	O(1)	Easy	Curated Top 75, bit, `apple`	AGAIN*** (2)
191	Number of 1 Bits	Python	O(1)	O(1)	Easy	Curated Top 75, apple	OK*
201	Bitwise AND of Numbers Range	Python	O(1)	O(1)	Medium		AGAIN (not start)
231	Power of Two	Python	O(1)	O(1)	Easy	good basic, Bit Manipulation ,`amazon`	OK*** (3)
260	Single Number III	Python	O(n)	O(1)	Medium	`xor`, `^=`, `^`	AGAIN*
268	Missing Number	Python	O(n)	O(1)	Medium	Curated Top 75, `xor`,`amazon`,`fb`	OK* (2)
318	Maximum Product of Word Lengths	Python	O(n) ~ O(n^2)	O(n)	Medium	Bit Manipulation, Counting Sort, Pruning	AGAIN (not start)
342	Power of Four	Python	O(1)	O(1)	Easy	`power of num`	OK*
371	Sum of Two Integers	Python	O(1)	O(1)	Medium	Curated Top 75, `good basic`, `fb`	AGAIN********* (5) (bit op not start)
389	Find the Difference	Python	O(n)	O(1)	Easy	`amazon`	OK (2)
393	UTF-8 Validation	Python	O(n)	O(1)	Medium	`utf-8 encoding`, `google`, `fb`	AGAIN**** (not start*) (5)
401	Binary Watch	Python	O(1)	O(1)	Easy		OK*
421	Maximum XOR of Two Numbers in an Array	Python	O(n)	O(n)	Medium		AGAIN (not start)
461	Hamming Distance	Python	O(1)	O(1)	Easy	`fb`	OK* (2)
462	Minimum Moves to Equal Array Elements II	Python	O(n) on average	O(1)	Medium		AGAIN*
477	Total Hamming Distance	Python	O(n)	O(1)	Medium	bit manipulation, `fb`	AGAIN****** (not start*) (4)
645	Set Mismatch	Python	O(n)	O(1)	Easy	`amazon`	OK* (3)
693	Binary Number with Alternating Bits	Python	O(1)	O(1)	Easy	`trick`	AGAIN*
762	Prime Number of Set Bits in Binary Representation	Python	O(1)	O(1)	Easy	`basic`,`Bit_Manipulation`, `prime number`, `amazon`	OK* (4)
868	Binary Gap	Python	O(1)	O(1)	Easy	`trick`, `linear scan`	AGAIN*
898	Bitwise ORs of Subarrays	Python	O(n)	O(1)	Medium		AGAIN (not start)
1573	Number of Ways to Split a String	Python	O(n)	O(1)	Medium	`amazon`, binary	AGAIN** (not start)
1915	Number of Wonderful Substrings	Python	O(n)	O(1)	Medium	bit mask, bit, prefix sum, dp, `amazon`	AGAIN*** (2) (not start)

String

#	Title	Solution	Time	Space	Difficulty	Status, Note	Status
005	Longest Palindromic Substring	python	O(n)	O(n)	Medium	Curated Top 75, LC 647, good trick, 2 pointer, recursive, `Manacher's Algorithm`, LC 100 like, `DP`, `UBER`, `amazon`, `fb`	AGAIN************** (8)(MUST)
006	ZigZag Conversion	python	O(n)	O(1)	Easy		AGAIN (not start)
008	String to Integer (atoi)	python	O(n)	O(1)	Medium	string op, `regular expression`,`UBER`, `amazon`, `fb`	AGAIN***** (5)
014	Longest Common Prefix	python	O(n k)*	O(1)	Easy	`good basic`	OK*
028	Implement strStr()	python	O(n + k)	O(k)	Easy	`KMP Algorithm`, `fb`	OK (3)
038	Count and Say	python	O(n 2^n)*	O(2^n)	Easy	`recursion`, `iteration`, basic, `fb`	AGAIN*********** (5)
043	Multiply Strings	python	O(m n)*	O(m + n)	Medium	`twitter`, `fb`	AGAIN*** (3)
058	Length of Last Word	python	O(n)	O(1)	Easy		OK
067	Add Binary	python	O(n)	O(1)	Easy	bit op, `good basic`, `fb`, `amazon`	OK***** (6) (but again)
076	Minimum Window Substring	python			Hard	`Curated Top 75`	AGAIN******* (2) (not start)
125	Valid Palindrome	python	O(n)	O(1)	Easy	Curated Top 75, LC 680, `amazon`,`fb`	OK
151	Reverse Words in a String	python	O(n)	O(1)	Medium	`amazon`,`fb`	OK (2)
161	One Edit Distance	python	O(m + n)	O(1)	Medium	🔒, trick, recursion, string, , `fb`	AGAIN ******** (6)(AGAIN)
165	Compare Version Numbers	python	O(n)	O(1)	Medium	good basic, string,`amazon`, `apple`	OK** (5)
186	Reverse Words in a String II	python	O(n)	O(1)	Medium	LC 151, LC 557, 🔒, `M$`,`UBER`, `amazon`	AGAIN* (3)
242	Valid Anagram	python	O(n)	O(1)	Easy	Curated Top 75, LintCode,`amazon`,`fb`	OK
271	Encode and Decode Strings	python	O(n)	O(1)	Medium	Curated Top 75, decode-encode, design, check `# 394 Decode String` ,🔒, `google`	AGAIN** (2)
306	Addictive Number	python	O(n^3)	O(n)	Medium		AGAIN (not start*)
340	Longest Substring with At Most K Distinct Characters	python	O(n^3)	O(n)	Hard	string, sliding window, `google`	not start
383	Ransom Note	python	O(n)	O(1)	Easy	EPI, apple	OK*
405	Convert a Number to Hexadecimal	python	O(n)	O(1)	Easy	`basics` `decimal -> Hexadecimal`	AGAIN
408	Valid Word Abbreviation	python	O(n)	O(1)	Easy	🔒	AGAIN (not start)
415	Add Strings	python	O(n)	O(1)	Easy	`good basic`, `add xxx to sum`, `Airbnb`, `google`, `fb`	OK****** (4)
434	Number of Segments in a String	python	O(n)	O(1)	Easy		OK
443	String Compression	python	O(n)	O(1)	Easy	shoptify, `basics`	AGAIN**
459	Repeated Substring Pattern	python	O(n)	O(n)	Easy	good basic, string, `KMP Algorithm`, `amazon`	OK*** (6)
468	Validate IP Address	python	O(1)	O(1)	Medium	`ip basic`,`string`,`twitter`, `fb`, `amazon`	AGAIN****** (5)
482	License Key Formatting	python	O(n)	O(1)	Easy	string, basic, `google`	OK** (3) (again)
520	Detect Capital	python	O(l)	O(1)	Easy		OK
521	Longest Uncommon Subsequence I	python	O(min(a, b))	O(1)	Easy		OK*
522	Longest Uncommon Subsequence II	python	O(l n^2)*	O(1)	Medium	Sort	AGAIN (not start)
524	Longest Word in Dictionary through Deleting	python	O((d l) * logd)*	O(1)	Medium	Sort, `google`	AGAIN (not start)
539	Minimum Time Difference	python	O(nlogn)	O(n)	Medium	`basic`, `map & zip trick`	AGAIN**
541	Reverse String II	python	O(n)	O(1)	Easy		AGAIN*
551	Student Attendance Record I	python	O(n)	O(1)	Easy		OK
556	Next Greater Element III	python	O(1)	O(1)	Medium		AGAIN (not start)
557	Reverse Words in a String III	python	O(n)	O(1)	Easy		OK
616	Add Bold Tag in String	python	O(n d * l)*	O(n)	Medium	🔒, `google`	AGAIN (not start)
647	Palindromic Substrings	python	O(n)	O(n)	Medium	Curated Top 75, LC 005, greedy, DP, expand from center, 2 pointers, `good basic`,`Manacher's Algorithm`, `Linkedin`,`amazon`,`fb`	OK******* (7) (MUST)
648	Replace Words	python	O(n)	O(t)	Medium	Trie, `good basic`	OK*
657	Judge Route Circle	python	O(n)	O(1)	Easy		OK
678	Valid Parenthesis String	python	O(n)	O(1)	Medium		AGAIN**
680	Valid Palindrome II	python	O(n)	O(1)	Easy	LC 125, two pointers, `good basic`, Palindrome, `string`, `fb`	AGAIN******** (3)
681	Next Closest Time	python	O(1)	O(1)	Medium	`subset of set`, `<=`,`strptime`, `google`,`fb`	OK*** (5)
686	Repeated String Match	python	O(n + m)	O(1)	Medium	brute force, string, string match, `Rabin-Karp Algorithm`, `google`	AGAIN**** (3)
696	Count Binary Substrings	python	O(n)	O(1)	Easy	good trick, linear scan, group sub-string, `amazon`	AGAIN******* (3) (MUST)
720	Longest Word in Dictionary	python	O(n)	O(t)	Easy	Trie	AGAIN (not start)
722	Remove Comments	python	O(n)	O(k)	Medium		AGAIN (not start)
751	IP to CIDR	python	O(n)	O(1)	Medium	`ip`	AGAIN (not start*)
758	Bold Words in String	python	O(n l)*	O(t)	Easy	🔒, variant of Add Bold Tag in String	AGAIN (not start)
791	Custom Sort String	python	O(n)	O(1)	Medium	`good basic`, sort, counter, `amazon`, `fb`	AGAIN************ (7) (MUST)
796	Rotate String	python	O(n)	O(1)	Easy	good basic, `KMP Algorithm`, `Rabin-Karp Algorithm`,`amazon`	OK**** (2)(but again)
804	Unique Morse Code Words	python	O(n)	O(n)	Easy		OK*
806	Number of Lines To Write String	python	O(n)	O(1)	Easy		OK*
809	Expressive Words	python	O(n + s)	O(l + s)	Medium		AGAIN (not start)
816	Ambiguous Coordinates	python	O(n^4)	O(n)	Medium		AGAIN (not start*)
819	Most Common Word	python	O(m + n)	O(m + n)	Easy	`regular expression`, `amazon`	OK** (2)
820	Short Encoding of Words	python	O(n)	O(t)	Medium	Trie	AGAIN (not start)
824	Goat Latin	python	O(n + w^2)	O(l)	Easy	`string basic`, `fb`	OK
828	Count Unique Characters of All Substrings of a Given String	python	O(n + w^2)	O(l)	Hard	LC 1248, dp, `string`, `amazon`	AGAIN*** (2)
831	Masking Personal Information	python	O(1)	O(1)	Medium	`regular expression`	OK*
833	Find And Replace in String	python	O(n + m)	O(n)	Medium	Union Find	AGAIN (not start)
848	Shifting Letters	python	O(n)	O(1)	Medium	`remainder`, `basic`	AGAIN**
859	Buddy Strings	python	O(n)	O(1)	Easy		AGAIN*
880	Decoded String at Index	python	O(n)	O(1)	Medium	`trick`	AGAIN (not start**)
884	Uncommon Words from Two Sentences	python	O(m + n)	O(m + n)	Easy	`collections Counter`, `trick`	OK*
890	Find and Replace Pattern	python	O(n l)*	O(1)	Medium		AGAIN (not start)
893	Groups of Special-Equivalent Strings	python	O(n l)*	O(n)	Easy		AGAIN*
916	Word Subsets	python	O(m + n)	O(1)	Medium		AGAIN (not start)
917	Reverse Only Letters	python	O(n)	O(1)	Easy	`basic`,`stack`,`pointer`	OK*
925	Long Pressed Name	python	O(n)	O(1)	Easy	`two pointer`, `basic`, `trick`	AGAIN*
929	Unique Email Addresses	python	O(n l)*	O(n l)*	Easy		OK
939	Minimum Area Rectangle	python	O(n^1.5) on average	O(n)	Medium		OK*
942	DI String Match	python	O(n)	O(1)	Easy		AGAIN (not start)
944	Delete Columns to Make Sorted	python	O(n l)*	O(1)	Medium		AGAIN (not start)
953	Verifying an Alien Dictionary	python	O(n l)*	O(1)	Easy		AGAIN (not start)
955	Delete Columns to Make Sorted II	python	O(n l)*	O(n)	Medium		AGAIN (not start)
1119	Remove Vowels from a String	python	O(n l)*	O(n)	Easy	`amazon`	OK

Queue

#	Title	Solution	Time	Space	Difficulty	Tag	Note
281	Zigzag Iterator	Python	O(n)	O(k)	Medium	`good basic`, queue, 🔒, `google`,`fb`	AGAIN******* (5)
346	Moving Average from Data Stream	Python	O(1)	O(w)	Easy	🔒, queue, `google`, `fb`	OK** (6)
933	Number of Recent Calls	Python	O(1) on average	O(w)	Easy		AGAIN**
622	Design Circular Queue	Python			Medium	`good basic`, array, linked list, design, `circular queue`,`amazon`,`fb`, apple, airbnb, m$	AGAIN************ (3) (MUST)
239	Sliding Window Maximum	Python			Hard	sliding window, heap, deque, queue,`amazon`, `google`	AGAIN********* (4)

Math

#	Title	Solution	Time	Space	Difficulty	Note	Status
007	Reverse Integer	Python	O(1)	O(1)	Medium	`0x7FFFFFFF`, amazon, apple	OK* (3)
009	Palindrome Number	Python	O(1)	O(1)	Easy	amazon	OK
012	Integer to Roman	Python	O(n)	O(1)	Medium	`math basic`,`twitter`, `fb`, amazon, math	AGAIN****** (4)
013	Roman to Integer	Python	O(n)	O(1)	Easy	`UBER`,`amazon`, `fb`	AGAIN***** (4)
029	Divide Two Integers	Python	O(1)	O(1)	Medium	`binary search`,`trick`,`fb`	AGAIN***** (3)
050	Pow(x, n)	Python	O(1)	O(1)	Medium	`good trick`,`amazon`, `fb`, recursion	AGAIN****** (4)
060	Permutation Sequence	Python	O(n^2)	O(n)	Medium	`Cantor Ordering`,trick ,`amazon`	AGAIN*** (2)
089	Gray Code	Python	O(2^n)	O(1)	Medium	bit op, math, `amazon`	AGAIN ********** (6)
166	Fraction to Recurring Decimal	Python	O(logn)	O(1)	Medium		AGAIN (not start)
168	Excel Sheet Column Title	Python	O(logn)	O(1)	Easy	trick, residual, math, AGAIN,`fb`	AGAIN****** (5)
171	Excel Sheet Column Number	Python	O(n)	O(1)	Easy		AGAIN (not start)
172	Factorial Trailing Zeroes	Python	O(1)	O(1)	Easy	`basic`, `iteration`, `recursion`	AGAIN* (2)
223	Rectangle Area	Python	O(1)	O(1)	Easy		AGAIN
258	Add Digits	Python	O(1)	O(1)	Easy		AGAIN
263	Ugly Number	Python	O(1)	O(1)	Easy	math	OK* (2)
273	Integer to English Words	Python	O(1)	O(1)	Hard	`amazon`, passed	not start
292	Nim Game	Python	O(1)	O(1)	Easy	LintCode	OK*
319	Bulb Switcher	Python	O(1)	O(1)	Medium		AGAIN
326	Power of Three	Python	O(1)	O(1)	Easy		OK
338	Counting Bits	Python	O(n)	O(n)	Medium	Curated Top 75	OK*
343	Integer Break	Python	O(logn)	O(1)	Medium	`trick`, `DP`	AGAIN* (2)
365	Water and Jug Problem	Python	O(logn)	O(1)	Medium	`Bézout's identity`	AGAIN (not start)
372	Super Pow	Python	O(n)	O(1)	Medium		AGAIN
382	Linked List Random Node	Python	O(n)	O(1)	Medium	`Reservoir Sampling`	AGAIN (not start)
386	Lexicographical Numbers	Python	O(n)	O(1)	Medium		AGAIN (not start)
390	Elimination Game	Python	O(logn)	O(1)	Medium		AGAIN (not start)
398	Random Pick Index	Python	O(n)	O(1)	Medium	`Reservoir Sampling` , `fb`	OK* (4)
400	Nth Digit	Python	O(logn)	O(1)	Easy		AGAIN
413	Arithmetic Slices	Python	O(n)	O(1)	Medium	sliding window, `amazon`	OK*** (1) (but again)
423	Reconstruct Original Digits from English	Python	O(n)	O(1)	Medium	GCJ2016 - Round 1B	AGAIN (not start)
441	Arranging Coins	Python	O(nlogn)	O(1)	Easy	Binary Search	OK
453	Minimum Moves to Equal Array Elements	Python	O(n)	O(1)	Easy		AGAIN
458	Poor Pigs	Python	O(n)	O(1)	Easy		AGAIN
469	Convex Polygon	Python	O(n)	O(1)	Medium	🔒	AGAIN (not start)
470	Implement Rand10() Using Rand7()	Python	O(1)	O(1)	Medium		AGAIN (not start)
478	Generate Random Point in a Circle	Python	O(1)	O(1)	Medium		AGAIN (not start)
497	Random Point in Non-overlapping Rectangles	Python	ctor: O(n) pick: O(logn)	O(n)	Medium		AGAIN (not start)
504	Base 7	Python	binary, math, good basic	O(n)	Easy		AGAIN******** (1)
519	Random Flip Matrix	Python	ctor: O(1) pick: O(1) reset: O(n)	O(n)	Medium		AGAIN (not start)
528	Random Pick with Weight	Python	ctor: O(n) pick: O(logn)	O(n)	Medium		AGAIN (not start)
537	Complex Number Multiplication	Python	O(1)	O(1)	Medium	math, `amazon`	OK (3)
553	Optimal Division	Python	O(n)	O(1)	Medium	string, math, `amazon`	OK* (4)
573	Squirrel Simulation	Python	O(n)	O(1)	Medium	🔒	AGAIN (not start)
592	Fraction Addition and Subtraction	Python	O(nlogx)	O(n)	Medium		AGAIN
593	Valid Square	Python	O(1)	O(1)	Medium		AGAIN
598	Range Addition II	Python	O(p)	O(1)	Easy		AGAIN
625	Minimum Factorization	Python	O(loga)	O(1)	Medium	🔒	OK*
628	Maximum Product of Three Numbers	Python	O(n)	O(1)	Easy	`amazon`	OK (2)
633	Sum of Square Numbers	Python	O(sqrt(c) logc)*	O(1)	Easy		OK*
634	Find the Derangement of An Array	Python	O(n)	O(1)	Medium	🔒	AGAIN (not start)
640	Solve the Equation	Python	O(n)	O(n)	Medium	math, regular expression, `amazon`	AGAIN*** (3)
651	4 Keys Keyboard	Python	O(1)	O(1)	Medium	🔒, Math, DP	AGAIN (not start)
672	Bulb Switcher II	Python	O(1)	O(1)	Medium		AGAIN (not start)
728	Self Dividing Numbers	Python	O(n)	O(1)	Medium		AGAIN
754	Reach a Number	Python	O(logn)	O(1)	Medium		OK*
775	Global and Local Inversions	Python	O(n)	O(1)	Medium	trick, math, string, `amazon`	AGAIN** (not start) (3)
779	K-th Symbol in Grammar	Python	O(1)	O(1)	Medium	math, brute force, binary, recursion, FB, amazon	AGAIN*** (1)
781	Rabbits in Forest	Python	O(n)	O(n)	Medium		AGAIN (not start)
789	Escape The Ghosts	Python	O(n)	O(1)	Medium		AGAIN
800	Similar RGB Color	Python	O(1)	O(1)	Easy	🔒	AGAIN (not start)
812	Largest Triangle Area	Python	O(n^3)	O(1)	Easy		AGAIN (not start)
829	Consecutive Numbers Sum	Python	O(sqrt(n))	O(1)	Medium		AGAIN
836	Rectangle Overlap	Python	O(1)	O(1)	Easy	similar as 223. Rectangle Area, `amazon`	AGAIN (2)
858	Mirror Reflection	Python	O(1)	O(1)	Medium		AGAIN (not start)
867	Prime Palindrome	Python	O(n^(1/2) (logn + n^(1/2)))*	O(logn)	Medium		AGAIN***
883	Projection Area of 3D Shapes	Python	O(n^2)	O(1)	Easy		AGAIN
891	Sum of Subsequence Widths	Python	O(n^2)	O(1)	Hard	`amazon`	AGAIN (not start)
907	Sum of Subarray Minimums	Python	O(n)	O(n)	Medium	trick, LC 084, LC 2104, Ascending Stack, `amazon`	AGAIN**** (1)
908	Smallest Range I	Python	O(n)	O(1)	Easy		OK* (2)
910	Smallest Range II	Python	O(nlogn)	O(1)	Medium		AGAIN (not start)
914	X of a Kind in a Deck of Cards	Python	O(n (logn)^2)*	O(n)	Easy		AGAIN (not start)
963	Minimum Area Rectangle II	Python	O(n^2) ~ O(n^3)	O(n^2)	Medium		AGAIN (not start)
970	Powerful Integers	Python	O((logn)^2)	O(r)	Easy	`basic`	AGAIN* (2)
517	Super Washing Machines	Python			Hard	`amazon`	AGAIN (not start)
1342	Number of Steps to Reduce a Number to Zero	Python			easy	`gra*`	ok
1492	The kth Factor of n	Python			Medium	`amazon`	AGAIN (not start)
1979	Find Greatest Common Divisor of Array	Python			Easy	GCD	not start

Sort

#	Title	Solution	Time	Space	Difficulty	Note	Status
075	Sort Colors	Python	O(n)	O(1)	Medium	sorting, Tri Partition,`two pointers`, `M$`, `fb`	OK** (4)
088	Merge Sorted Array	Python	O(n)	O(1)	Easy	`good basic`, merge, sort,`two pointers`, `M$`, `amazon`,`fb`	AGAIN************* (7) (MUST)
128	Longest Consecutive Sequence	Python			Medium	Curated Top 75, 2 pointers, sort, sliding window, `amazon`	AGAIN*********** (4) (MUST)
147	Insertion Sort List	Python	O(n^2)	O(1)	Medium	`trick`	AGAIN* (2)
148	Sort List	Python	O(nlogn)	O(logn)	Medium	`basic`, check `# 21 Merge Two Sorted Lists`	AGAIN** (2)
179	Largest Number	Python	O(nlogn)	O(1)	Medium	good basic, sort with lambda,`amazon`	AGAIN************ (3)
252	Meeting Rooms	Python	O(nlogn)	O(n)	Easy	Curated Top 75, 🔒,`UBER`,`amazon`, `fb`	OK*** (3) (but again)
253	Meeting Rooms II	Python	O(nlogn)	O(n)	Medium	Curated Top 75, 🔒, sort, priority queue (min-heap),`scanning line`, `trick`,`booking.com`,`good`,`UBER`, `amazon`,`google`,`fb`	AGAIN************ (5) (MUST)
274	H-Index	Python	O(n)	O(n)	Medium	Counting Sort,`good trick`, `fb`	AGAIN***** (3)
280	Wiggle Sort	Python	O(n)	O(1)	Medium	🔒,`google`,`fb`	OK*** (3)
324	Wiggle Sort II	Python	O(n) on average	O(1)	Medium	variant of Sort Colors , Tri Partition, `google`	AGAIN** (2)
347	Top K Frequent Elements	Python	O(n)	O(n)	Medium	Curated Top 75, Quick Select, Heap, Bucket Sort,`Yelp`,`amazon`,`fb`	OK* (3)
406	Queue Reconstruction by Height	Python	O(n sqrt(n))*	O(n)	Medium	`basic`,`trick`, `sort by key`, `insert`, `google`	AGAIN********* (5)
451	Sort Characters By Frequency	Python	O(n)	O(n)	Medium	`collections.Counter(s).most_common`,`sorted(count_dict.items() with lambda`,good basic, `amazon`	OK* (4)
692	Top K Frequent Words	Python	O(n + klogk) on average	O(n)	Medium	`good basic`,Quick Select, Heap, Bucket Sort, `heapq`, `yelp`, `UBER`,`amazon`,`fb`	OK***** (5)
937	Reorder Data in Log Files	Python	O(nlogn l)*	O(l)	Easy	good basic, sort, `string`, `amazon`	OK**** (3)(again!!!)
969	Pancake Sorting	Python	O(n^2)	O(l)	Medium	`fb`, sorting	AGAIN********** (4)
973	K Closest Points to Origin	Python	O(n) on average	O(1)	Medium	sort with lambda, Quick Select, Heap, `amazon`	OK* (3)
976	Largest Perimeter Triangle	Python	O(nlogn)	O(1)	Easy		OK*
1152	Analyze User Website Visit Pattern	Python	O(nlogn)	O(1)	Medium	itertools.combinations, sort, brute force, set, `amazon`	AGAIN***** (2) (not start)
2021	Brightest Position on Street	Python	O(nlogn)	O(1)	Medium	LC 253 meeting room II, priority queue (min-heap), scanning line, trick, `amazon`	AGAIN*********** (3) (MUST)

Two Pointers

#	Title	Solution	Time	Space	Difficulty	Note	Status
019	Remove Nth Node From End of List	Python	O(n)	O(1)	Medium	Curated Top 75, good basic, `linked list`,`two pointers`,`fb`	AGAIN********** (4) (MUST)
042	Trapping Rain Water	Python			Hard	scan, dp, trick, two pointer, `amazon`, `apple`	AGAIN*** (2) (not start)
086	Partition List	Python	O(n)	O(1)	Medium		OK*
141	Linked List Cycle	Python	O(n)	O(1)	Easy	Curated Top 75, `basic`,`amazon`, `fb`, linked list, 2 pointers, check #142	OK** (5)
142	Linked List Cycle II	Python	O(n)	O(1)	Medium	linked list, 2 pointers, check #141	AGAIN****** (4) (again!)
143	Reorder List	Python	O(n)	O(1)	Medium	Curated Top 75, LC 021, 206, 876, `good trick`,`inverse linkedlist`, `merge linkedlist` ,`fb`	AGAIN********** (4) (MUST)
167	Two Sum II - Input array is sorted	Python	O(n)	O(1)	Easy	two pointer, dict, binary search,`good basic`, `amazon`	OK* (6)
259	3Sum Smaller	Python	O(n^2)	O(1)	Medium	🔒, LintCode, `good trick`, `google`, `fb`, check `#015 3 Sum`, check `#001 two sum`	AGAIN******** (4)
283	Move Zeroes	Python	O(n)	O(1)	Easy	`basic`, `trick`, ,`two pointers`,`Shopee`,`fb`	AGAIN** (4)
344	Reverse String	Python	O(n)	O(1)	Easy		OK
345	Reverse Vowels of a String	Python	O(n)	O(1)	Easy	`google`	OK
349	Intersection of Two Arrays	Python	O(m + n)	O(min(m, n))	Easy	EPI, Hash, Binary Search, `fb`	OK
350	Intersection of Two Arrays II	Python	O(m + n)	O(1)	Easy	EPI, Hash, Binary Search, `good basic`, `fb`	OK** (3)
360	Sort Transformed Array	Python	O(n)	O(1)	Medium	`trick`,🔒,`google` ,`fb`	AGAIN*** (3)
457	Circular Array Loop	Python	O(n)	O(1)	Medium		AGAIN (not start)
567	Permutation in String	Python	O(n)	O(1)	Medium	`Collections.counter good basic`,`sliding window`,`substring`, `good basic`,`M$`, `fb`	OK********* (7)
611	Valid Triangle Number	Python	O(n^2)	O(1)	Medium		AGAIN (not start)
777	Swap Adjacent in LR String	Python	O(n)	O(1)	Medium		AGAIN (not start)
826	Most Profit Assigning Work	Python	O(mlogm + nlogn)	O(n)	Medium	`trick`, `good basic`, `zip+sorted`	OK*
844	Backspace String Compare	Python	O(m + n)	O(1)	Easy	`good basic`,`stack`,`google`, `fb`	OK* (4)
876	Middle of the Linked List	Python	O(n)	O(1)	Easy	basic, amazon, apple, google, 2 pointers, linkedlist	OK* (2)
904	Fruit Into Baskets	Python	O(n)	O(1)	Medium		AGAIN (not start)
930	Binary Subarrays With Sum	Python	O(n)	O(1)	Medium	`trick`	AGAIN* (2) (not start)
977	Squares of a Sorted Array	Python	O(n)	O(1)	Easy		OK
1151	Minimum Swaps to Group All 1's Together	Python	O(n)	O(1)	Medium	good basic, 2 pointers, Deque (Double-ended Queue), `amazon`	AGAIN***** (not start )
1963	Minimum Number of Swaps to Make the String Balanced	Python	O(n)	O(h)	Medium	good basic, greedy, stack, 2 pointers, amazon, fb, m$	AGAIN******** (2)
2104	Sum of Subarray Ranges	Python	O(n)	O(1)	Medium	LC 907, monotonic stack, brute force, 2 pointers, dp, `amazon`	AGAIN******* (3)

Recursion

#	Title	Solution	Time	Space	Difficulty	Note	Status
10	Regular Expression Matching	Python	O(n)	O(h)	Hard	recursive, dp, `amazon`	AGAIN (not start)
095	Unique Binary Search Trees II	Python	O(4^n / n^(3/2)	O(4^n / n^(3/2)	Medium	recursion, BST, amazon, google, apple	AGAIN!!! (1)(good trick)
098	Validate Binary Search Tree	Python	O(n)	O(1)	Medium	Curated Top 75, recursion, bfs, dfs,`BST`,`M$`,`amazon`, `fb`	AGAIN****************** (10)
100	Same Tree	Python	O(n)	O(h)	Easy	Curated Top 75, recursion, dfs, bfs, `good basic`,`amazon`	OK****** (4) (but again)
104	Maximum Depth of Binary Tree	Python	O(n)	O(h)	Easy	Curated Top 75, DFS, BFS, good basic,`amazon`, LC 111	OK****** (3) (but again)
105	Construct Binary Tree from Preorder and Inorder Traversal	Python	O(n)	O(n)	Medium	Curated Top 75, `trick`, check # 106,`BST`,`M$`, `fb`	AGAIN********* (8)
106	Construct Binary Tree from Inorder and Postorder Traversal	Python	O(n)	O(n)	Medium	`trick`,check # 105,`BST`,`M$`, `fb`	AGAIN******* (6)
108	Convert Sorted Array to Binary Search Tree	Python	O(n)	O(logn)	Medium	`good concept`	AGAIN*
109	Convert Sorted List to Binary Search Tree	Python	O(n)	O(logn)	Medium	`list`,`BST`,`good concept`, `fb`	AGAIN*** (3)
110	Balanced Binary Tree	Python	O(n)	O(h)	Easy	`good trick`,`dfs`, `bloomberg`,`amazon` ,`fb`, google, spotify	AGAIN********** (4)
111	Minimum Depth of Binary Tree	Python	O(n)	O(h)	Easy	`good basic`,`dfs`,`BST`,`amazon`,`fb`, LC 104	AGAIN******** (4)
114	Flatten Binary Tree to Linked List	Python	O(n)	O(h)	Medium	`BST`, `dfs`, `M$`, `fb`	AGAIN**** (4)
116	Populating Next Right Pointers in Each Node	Python	O(n)	O(1)	Medium	bfs, dfs, tree, recursion ,AGAIN,`fb`, amazon	AGAIN****** (5)
117	Populating Next Right Pointers in Each Node II	Python	O(n)	O(h)	Medium	`Populating Next Right Pointers in Each Node I`, bfs, linked list, `amazon`, `fb`	AGAIN****** (3)
129	Sum Root to Leaf Numbers	Python	O(n)	O(h)	Medium	`trick`,`BST`, `dfs`, `fb`	AGAIN*** (4)
156	Binary Tree Upside Down	Python	O(n)	O(1)	Medium	🔒	AGAIN (not start)
241	Different Ways to Add Parentheses	Python	O(n 4^n / n^(3/2))*	O(n 4^n / n^(3/2))*	Medium		AGAIN (not start)
298	Binary Tree Longest Consecutive Sequence	Python	O(n)	O(h)	Medium	bfs, dfs, tree, 🔒, `google`	OK***** (3)
333	Largest BST Subtree	Python	O(n)	O(h)	Medium	🔒	AGAIN (not start)
337	House Robber III	Python	O(n) O(h)	Medium	amazon, google	AGAIN (not start)
395	Longest Substring with At Least K Repeating Characters	Python	O(n)	O(1)	Medium	`AGAIN`,`recursion`, `good trick`,`fb`	AGAIN************ (4)
404	Sum of Left Leaves	Python	O(n)	O(h)	Easy, tree, bfs, dfs	`fb`	OK**** (3)
437	Path Sum III	Python	O(n)	O(h)	Medium	`good trick`,`UBER`, `AMAZON`, `fb`	AGAIN*** (3)
544	Output Contest Matches	Python	O(n)	O(n)	Medium		AGAIN
549	Binary Tree Longest Consecutive Sequence II	Python	O(n)	O(h)	Medium	🔒	AGAIN (not start)
669	Trim a Binary Search Tree	Python	O(n)	O(h)	Medium	good basic, BST, dfs, recursion,`amazon`	AGAIN******* (4)
671	Second Minimum Node In a Binary Tree	Python	O(n)	O(h)	Easy	dfs,tree	OK* (2)

Binary Search

#	Title	Solution	Time	Space	Difficulty	Tag, Note	Status
033	Search in Rotated Sorted Array	Python			Medium	Curated Top 75, `binary search`,`good basic` ,check `# 81 Search in Rotated Sorted Array II`,`UBER`,`amazon`,`fb`	AGAIN************ (5) (MUST)
034	Find First and Last Position of Element in Sorted Array	Python	O(n)	O(1)	Medium	binary search, LC top 100 like, `amazon`, `fb`, google, apple, uber	AGAIN************** (4) (MUST)
034	Search for a Range	Python	O(logn)	O(1)	Medium		AGAIN*
035	Search Insert Position	Python	O(logn)	O(1)	Medium		AGAIN
069	Sqrt(x)	Python	O(logn)	O(1)	Medium	math, binary search,`amazon`,`fb`	OK* (4)
074	Search a 2D Matrix	Python	O(logm + logn)	O(1)	Medium	binary search in 2D matrix,`amazon`	OK* (2)
081	Search in Rotated Sorted Array II	Python	O(logn)	O(1)	Medium	`binary search`,check `# 33 Search in Rotated Sorted Array` first,`array`, `fb`, amazon, linkedin	OK***** (6)
153	Find Minimum in Rotated Sorted Array	Python	O(logn)	O(1)	Medium	Curated Top 75, binary search, good basic,`amazon`	AGAIN****** (2)
162	Find Peak Element	Python	O(logn)	O(1)	Medium	good trick, recursive binary search,`M$`, `google`, `fb`	AGAIN********** (5)
222	Count Complete Tree Nodes	Python	O((logn)^2)	O(1)	Medium		AGAIN (not start)
275	H-Index II	Python	O(logn)	O(1)	Medium	similar as `# 274 H-Index`, Binary Search, `fb`	AGAIN**** (3)
278	First Bad Version	Python	O(logn)	O(1)	Easy	`good basic`,LintCode, `fb`	OK*** (5) (but again)
300	Longest Increasing Subsequence	Python	O(nlogn)	O(n)	Medium	Curated Top 75, array, binary search,`DP good basic`, `binary search`, LintCode, DP,`amazon`,`fb`	AGAIN********** (8)
367	Valid Perfect Square	Python	O(logn)	O(1)	Easy	good basic, similar as `# 69 Sqrt(x)`	OK* (3)
374	Guess Number Higher or Lower	Python	O(logn)	O(1)	Easy		OK*
410	Split Array Largest Sum	Python	O(logn)	O(1)	Hard		AGAIN (not start)
436	Find Right Interval	Python	O(nlogn)	O(n)	Medium		AGAIN (not start)
475	Heaters	Python	O((m + n) logn)*	O(1)	Easy		AGAIN (not start)
540	Single Element in a Sorted Array	Python	O(logn)	O(1)	Medium		OK*
658	Find K Closest Elements	Python	O(logn + k)	O(1)	Medium	`good trick`, sorting, stack, `two pointers`,`binary search`,`amazon`,`fb`, google	AGAIN ************** (5) (MUST)
744	Find Smallest Letter Greater Than Target	Python	O(logn)	O(1)	Easy		OK*
852	Peak Index in a Mountain Array	Python	O(logn)	O(1)	Easy	LC 162 Find Peak Element, `amazon`	OK* (2)
875	Koko Eating Bananas	Python	O(nlogr)	O(1)	Medium	binary search, good basic	AGAIN******* (3)
894	All Possible Full Binary Trees	Python	O(n 4^n / n^(3/2))*	O(n 4^n / n^(3/2))*	Medium		AGAIN (not start)
911	Online Election	Python	ctor: O(n) query : O(logn)	O(n)	Medium		AGAIN (not start)
1011	Capacity To Ship Packages Within D Days	Python			Medium	good trick, binary search, amazon, apple, fb, m$	AGAIN****** (2)
1889	Minimum Space Wasted From Packaging	Python			Hard	heap, prefix sum, binary search, amazon	AGAIN (not start)
2009	Minimum Number of Operations to Make Array Continuous	Python			Hard	binary search, sliding window, dequeue, bisect.bisect_right, amazon	AGAIN (not start)

Binary Search Tree

#	Title	Solution	Time	Space	Difficulty	Tag,Note	Status
220	Contains Duplicate III	python	O(nlogk)	O(k)	Medium		AGAIN (not start)
230	Kth Smallest Element in a BST	python	O(max(h, k))	O(min(h, k))	Medium	Curated Top 75, good basic BST basic, BST,`amazon`	OK********* (3) (but AGAIN)
235	Lowest Common Ancestor of a Binary Search Tree	python	O(h)	O(1)	Easy	Curated Top 75, BST, recursion, iteration, good basic, `LCA`, check `# 236 Lowest Common Ancestor of a Binary Tree`, `amazon`,`fb`	OK**************** (but again)(9)
270	Closest Binary Search Tree Value	python	O(h)	O(1)	Easy	`good basic` ,🔒, `M$`, BST, `google`,`fb`	OK***** (5)
285	Inorder Successor in BST	python	O(h)	O(1)	Medium	BST, dfs, good basic, 🔒,`amazon`,`fb`	OK** (4)
449	Serialize and Deserialize BST	python	O(n)	O(h)	Medium	LC 297, dfs, bfs, good trick,`serizlize deserizlize`, tree, `amazon`, `fb`	AGAIN************* (9) (MUST)
450	Delete Node in a BST	python	O(h)	O(h)	Medium	AGAIN, good trick, BST, tree, dfs	AGAIN****** (6) (but again)
530	Minimum Absolute Difference in BST	python	O(n)	O(h)	Easy		AGAIN*
700	Search in a Binary Search Tree	python	O(n)	O(h)	Easy	BST, good basic, recursion, iteration amazon	AGAIN*** (1)
776	Split BST	python	O(n)	O(h)	Medium	🔒, BST, tree, DFS, trick, basic, AGAIN ,`amazon`	AGAIN***** (5) (not start*)
783	Minimum Distance Between BST Nodes	python	O(n)	O(h)	Easy		OK*
426	Convert Binary Search Tree to Sorted Doubly Linked List	Python			Medium	,`linked list`, `good basic` `UBER`, `lyft`, `amazon`, `google`,`fb`	AGAIN***** (5)
968	Binary Tree Cameras	Python		O(n)	Hard	`amazon`, dfs, bst, dp, greedy, m$	AGAIN (not start)
1022	Sum of Root To Leaf Binary Numbers	Python		O(n)	Easy	good basic, LC 257, bst path, dfs, bfs,`amazon`	AGAIN******** (1) (MUST)
1597	Build Binary Expression Tree From Infix Expression	Python		O(n)	Hard	LC 224, recursive, iteration, stack, `amazon`, google, bst	AGAIN*** (1)

Breadth-First Search

#	Title	Solution	Time	Space	Difficulty	Tag	Status
102	Binary Tree Level Order Traversal	Python	O(n)	O(n)	Easy	Curated Top 75, `GOOD basic`, `dfs`, `bfs`,`UBER`, `apple`,`amazon`,`fb`	AGAIN******* (7) (must)
107	Binary Tree Level Order Traversal II	Python	O(n)	O(n)	Easy	same as `# 102 Binary Tree Level Order Traversal`	OK* (2)
103	Binary Tree Zigzag Level Order Traversal	Python	O(n)	O(n)	Medium	`amazon`,`fb`	OK
126	Word Ladder II	Python			Hard	complex, trick, dfs, bfs, dfs+bfs, check `# 127 Word Ladder`,`amazon`	AGAIN*** (3)
127	Word Ladder	Python	O(n d)*	O(d)	Hard/Medium	good basic, check #126 Word Ladder II, `bfs`, `UBER`, `amazon`, `M$`, `fb`	AGAIN************** (9)
130	Surrounded Regions	Python	O(m + n)		Medium	`bfs`, `dfs`,`union find`,good basic, `amazon`	AGAIN*********** (5)
133	Clone Graph	Python	O(n)	O(n)	Medium	Curated Top 75, good trick, `check #138 Copy List with Random Pointer` ,`graph`,`dfs`,`bfs`, copy, `UBER`, `google`,`amazon`,`fb`	AGAIN**************** (9) (MUST)
207	Course Schedule	Python	O(\|V\| + \|E\|)	O(\|E\|)	Medium	Curated Top 75, Topological Sort, backtrack, `good trick`,`dfs`, `bfs` , `amazon`,`fb`	AGAIN**************** (11) (MUST)
210	Course Schedule II	Python	O(\|V\| + \|E\|)	O(\|E\|)	Medium	Topological Sort,check `# 207 Course Schedule` first, `dfs`, `bfs` ,`amazon` ,`fb`	AGAIN********* (9) (again)
261	Graph Valid Tree	Python	O(\|V\| + \|E\|)	O(\|V\| + \|E\|)	Medium	Curated Top 75, AGAIN, bfs, dfs, grpah, 🔒, `graph`,`quick union`,`union find` ,`google`,`amazon`,`fb`	AGAIN************* (8)
286	Walls and Gates	Python	O(m n)*	O(g)	Medium	🔒, `dfs`, `bfs` , `good basic`, `google`,`amazon`,`FB`	AGAIN******** (7)
310	Minimum Height Trees	Python	O(n)	O(n)	Medium	`complex`	AGAIN (3) (not start)
433	Minimum Genetic Mutation	Python	O(n b)*	O(b)	Medium	check `# 127 Word Ladder`, `good basic`	AGAIN*** (3)
444	Sequence Reconstruction	Python	O(n s)*	O(n)	Medium	🔒 Topological Sort , `google`, `airbnb`	AGAIN** (3) (not start)
490	The Maze	Python	O(max(r, c) w)*	O(w)	Medium	`basic`, `bfs`, `dfs`,`amazon`,`fb`	AGAIN**** (5)
505	The Maze II	Python	O(max(r, c) wlogw)*	O(w)	Medium	`trick`,`bfs`,`dfs`,`AGAIN`, `google`, `fb`	AGAIN********* (6)
542	01 Matrix	Python	O(m n)*	O(m n)*	Medium	DP, `trick`,`queue`	AGAIN*** (3)
666	Path Sum IV	Python	O(n)	O(w)	Medium	🔒 Topological Sort	AGAIN* (3) (not start)
742	Closest Leaf in a Binary Tree	Python	O(n)	O(n)	Medium	AGAIN, Graph, bfs+dfs, search, `good trick`, `amazon`	AGAIN********** (6)
743	Network Delay Time	Python	O(\|E\| log\|V\|)*	O(\|E\|)	Medium	`Dijkstra's algorithm`	AGAIN (not start)
752	Open the Lock	Python	O(k n^k + d)*	O(k n^k + d)*	Medium	LC 863	AGAIN (not start)
787	Cheapest Flights Within K Stops	Python	O(\|E\| log\|V\|)*	O(\|E\|)	Medium	`Dijkstra's algorithm`, dfs, bfs, graph, priority queue,`amazon`, apple, google, airbnb	AGAIN****** (3) (not start)
815	Bus Routes	Python	O(\|E\| log\|V\|)*	O(\|E\|)	Hard	shortest route, graph, bfs,`amazon`	AGAIN*** (2) (not start)
886	Possible Bipartition	Python	O(\|V\| + \|E\|)	O(\|V\| + \|E\|)	Medium	check `# 785 Is Graph Bipartite?`,`graph`, `AGAIN`,`union find` ,`fb`	AGAIN********** (6)
934	Shortest Bridge	Python	O(n^2)	O(n^2)	Medium	BFS, DFS, `complex`	AGAIN (not start)
967	Numbers With Same Consecutive Differences	Python	O(2^n)	O(2^n)	Medium	`good trick`	AGAIN** (3)
675	Cut Off Trees for Golf Event	Python, Java			Hard	tree, BFS, complex, `amazon`	AGAIN (not start)
864	Shortest Path to Get All Keys	Python			Hard	BFS, `amazon`	AGAIN (not start)
994	Rotting Oranges	Python			Medium	BFS, dp `amazon`	OK** (2)
1162	As Far from Land as Possible	Python			Medium	dfs, bfs, good basic, `amazon`	AGAIN**** (3)
1730	Shortest Path to Get Food	Python			Medium	shortest path, bfs, `amazon`	OK (2)

Depth-First Search

#	Title	Solution	Time	Space	Difficulty	Tag	Status
112	Path Sum	Python, Scala	O(n)	O(h)	Easy	`good concept`, `amazon`, dfs	OK** (2)
113	Path Sum II	Python	O(n)	O(h)	Medium	dfs, LC `112 Path Sum`,`good basic`, `amazon`, `fb`	AGAIN****** (5)
199	Binary Tree Right Side View	Python	O(n)	O(h)	Medium	`good basic`, `dfs`, `bfs`,`apple`,`amazon`, `fb`	OK*** (5)
200	Number of Islands	Python	O(m n)*	O(m n)*	Medium	Curated Top 75, `bfs`, `dfs`,`good basic`,check `# 694, 711 Number of Distinct Islands`,`apple`, `Goldman Sachs`,`google`,`amazon`,`fb`	OK****** (6)
236	Lowest Common Ancestor of a Binary Tree	Python	O(n)	O(h)	Medium	`trick`,EPI, `LCA`,check `235 Lowest Common Ancestor of a Binary Search Tree`,`apple`,`amazon`,`linkedin`,`fb`	AGAIN************* (9)
247	Strobogrammatic Number II	Python	O(n^2 5^(n/2))*	O(n)	Medium	🔒,check `#246 Strobogrammatic Number`,`good trick`, `google`,`fb`	AGAIN******** (4)
250	Count Univalue Subtrees	Python	O(n)	O(h)	Medium	🔒	AGAIN (not start)
257	Binary Tree Paths	Python	O(n h)*	O(h)	Easy	good basic,`apple`, `google`, `amazon`, `fb`, bfs, dfs, bst	AGAIN********* (MUST) (6)
332	Reconstruct Itinerary	Python	O(t! / (n1! n2! * ... nk!))*	O(t)	Medium	`yelp`, `google`	AGAIN* (3) (not start)
339	Nested List Weight Sum	Python	O(n)	O(h)	Easy	🔒,`good basic`,`bfs`, `linkedin`, `fb`	AGAIN*** (3)
364	Nested List Weight Sum II	Python	O(n)	O(h)	Medium	🔒, `linkedin`	AGAIN*
366	Find Leaves of Binary Tree	Python	O(n)	O(h)	Medium	🔒, `linkedin`	AGAIN*
399	Evaluate Division	Python	O(q \|V\|!)*	O(e)	Medium	`union find`, `dfs`, `AGAIN`, `good trick` `google`, `fb`	AGAIN*********** (6)
417	Pacific Atlantic Water Flow	Python	O(m n)*	O(m n)*	Medium	Curated Top 75, 2 direction dfs, dfs, matrix, `m$`,`google`	AGAIN** (3)
464	Can I Win	Python	O(n!)	O(n)	Medium	`DP`, `linkedin`	AGAIN* (not start)
491	Increasing Subsequences	Python			Medium	`trick`,`dfs`,`dfs good trick`, `dp`,`yahoo` ,`fb`	AGAIN***** (2)
515	Find Largest Value in Each Tree Row	Python	O(n)	O(h)	Medium	`good basic`,`linkedin`	AGAIN* (3)
529	Minesweeper	Python			Medium	dfs, bfs, good basic, dfs, bfs,`amazon`	AGAIN**** (4)
547	Friend Circles	Python	O(n^2)	O(n)	Medium	graph, Union Find,dfs, bfs,check `# 733 Flood Fill`,`bloomberg` ,`fb`	AGAIN*** (3) (not start)
547	Number of Provinces	Python	O(n^2)	O(n)	Medium	dfs, bfs, graph, union find, good basic, apple, amazon	AGAIN************ (2) (MUST)
582	Kill Process	Python	O(n)	O(n)	Medium	🔒, DFS, BFS,`good basic` ,`bloomberg`, `amazon`	AGAIN***** (4)
638	Shopping Offers	Python	O(n 2^n)*	O(n)	Medium	`google`	AGAIN (not start*)
690	Employee Importance	Python	O(n)	O(h)	Easy	DFS, BFS,`good basic` ,`UBER`	OK** (3)
694	Number of Distinct Islands	Python	O(m n)*	O(m n)*	Medium	`#200, #711 Number of Islands` good pattern, dfs, 🔒, compare with `# 200 Number of Islands`, `amazon`	AGAIN******** (5)
695	Max Area of Island	Python	O(m n)*	O(m n)*	Easy	`amazon`, `microsoft`, `linkedin`, `basic`	AGAIN* (3)
711	Number of Distinct Islands II	Python, Java			Hard	complex, dfs, check `# 200, 694 Number of Distinct Islands`,`amazon`	OK*** (3)
721	Accounts Merge	Python	O(nlogn)	O(n)	Medium	dfs, Disjoint Set Union (DSU), `Union Find`,`path compression`, `complex`, `fb`, google, amazon, m$, apple, twitter	AGAIN******* (4) (not start)
733	Flood Fill	Python	O(m n)*	O(m n)*	Easy	`fb`, `amazon`, `good basic`	OK**** (5)
734	Sentence Similarity	Python	O(n + p)	O(p)	Easy	good basic, graph, `hash table`,`collections.defaultdict(set)` ,`google`	OK***** (4) (but again)
737	Sentence Similarity II	Python	O(m n)*	O(m n)*	Medium	dfs, union find, `google`	AGAIN**** (2)
756	Pyramid Transition Matrix	Python	O(a^b)	O(a^b)	Medium		AGAIN (3) (not start)
785	Is Graph Bipartite?	Python	O(\|V\| + \|E\|)	O(\|V\|)	Medium	`check #886 Possible Bipartition`,`AGAIN`,`graph`,`dfs`,`fb`, `amazon`	AGAIN*********** (6)
797	All Paths From Source to Target	Python	O(p + r n)*	O(n)	Medium	`graph`, `dfs classics`, `good basic`	AGAIN** (3)
802	Find Eventual Safe States	Python	O(\|V\| + \|E\|)	O(\|V\|)	Medium	`Topological Sort`	AGAIN (3) (not start)
841	Keys and Rooms	Python	O(n!)	O(n)	Medium	`google`, `bfs`, `dfs`, `good basic`	AGAIN*** (3)
851	Loud and Rich	Python	O(q + r)	O(q + r)	Medium	`amazon`,`defaultdict`, `good basic`	AGAIN*** (3)
1192	Critical Connections in a Network	Python	O(q + r)	O(q + r)	Hard	Tarjan's algorithm,dfs, graph, fb, amazon	AGAIN** (1) (not start)
1644	Lowest Common Ancestor of a Binary Tree II	Python	O(q + r)	O(q + r)	Medium	LCA, LC 236, m$, fb	AGAIN (not start)
1650	Lowest Common Ancestor of a Binary Tree III	Python	O(q + r)	O(q + r)	Medium	`parent node`, good trick, dfs, set, dict, LCA, LC 236, amazon, google, spotify m$, fb	AGAIN******** (2) (MUST)
1676	Lowest Common Ancestor of a Binary Tree IV	Python	O(q + r)	O(q + r)	Medium	LCA, LC 236, a m$	AGAIN (not start)

Backtracking

#	Title	Solution	Time	Space	Difficulty	Tag, Note	Status
017	Letter Combinations of a Phone Number	Python	O(n 4^n)*	O(n)	Medium	dfs, backtrack, `good trick`,`UBER`, `amazon`, `google`, `fb`	AGAIN************* (10) (MUST)
022	Generate Parentheses	Python	O(4^n / n^(3/2))	O(n)	Medium	LC 20, good basic, DFS, backtracking,`amazon`	OK******* (3) (but again)
039	Combination Sum	Python	O(k n^k)*	O(k)	Medium	backtrack,`dfs`,`good basic`,`UBER`, `airbnb`, `amazon`,`fb`	OK********* (7) (but again)
040	Combination Sum II	Python	O(k C(n, k))*	O(k)	Medium	similar as `#39 Combination Sum`	AGAIN*** (3) (again)
046	Permutations	Python	O(n n!)*	O(n)	Medium	backtrack, LC #77, 78, `good concept`, `M$`, `linkedin`, `amazon`,`fb`	OK*********** (4) (AGAIN, MUST)
047	Permutations II	Python	O(n n!)*	O(n)	Medium	similar as `#46 Permutations`, apple, amazon, m$	AGAIN (not start)
077	Combinations	Python	O(O(k C(n, k)))*	O(k)	Medium	good trick, backtrack	OK********** (4) (but again, MUST)
079	Word Search	Python	O(m n * l)*	O(l)	Medium	LC 212, Curated Top 75, back tracking,`good trick`,`dfs`,`bloomberg`, `M$`, `amazon`,`fb`	AGAIN*************** (10) (MUST)
093	Restore IP Addresses	Python	O(1)	O(1)	Medium	good trick,recursive,IP address,`amazon`	AGAIN****** (4)
078	Subsets	Python	O(n 2^n)*	O(1)	Medium	`good concept` , similar as, dfs, back track, `#90 Subsets II` , `UBER`, `amazon`, `fb`	AGAIN**************** (7) (MUST again!!!)
090	Subsets II	Python	O(n 2^n)*	O(1)	Medium	good basic,check `# 078 Subsets`, dfs, backtrack, `fb`	AGAIN********* (6)
131	Palindrome Partitioning	Python	O(n^2) ~ O(2^n)	O(n^2)	Medium	dfs, backtracking, good trick,`amazon`	AGAIN*********** (6) (MUST)
139	Word Break	Python	O(n l^2)*	O(n)	Medium	Curated Top 75, backtracking, dfs, `dp`,`trick`,`UBER`,`yahoo`,`amazon`, `google`,`fb`	AGAIN**************** (7) (MUST)
140	Word Break II	Python	O(n l^2)*	O(n)	Hard	good basic, LC 078, backtracking, dfs, `dp`,`trick`, `amazon`	AGAIN******** (2)
212	Word Search II	Python	O(m n * l)*	O(l)	Hard	Curated Top 75, LC 208, LC 079, hashset, hashmap, trie, backtrack with trie, `amazon`, fb, apple, twitter, uber, google, indeed	AGAIN********** (3)
216	Combination Sum III	Python	O(k C(n, k))*	O(k)	Medium		AGAIN*
254	Factor Combinations	Python	O(nlogn)	O(logn)	Medium	🔒	AGAIN (not start)
267	Palindrome Permutation II	Python	O(n n!)*	O(n)	Medium	🔒	AGAIN (not start*)
294	Flip Game II	Python	O(n + c^2)	O(c)	Medium	🔒, DP, Hash	AGAIN*
320	Generalized Abbreviation	Python	O(n 2^n)*	O(n)	Medium	🔒	AGAIN (not start*)
526	Beautiful Arrangement	Python	O(n!)	O(n)	Medium		AGAIN (not start*)
676	Implement Magic Dictionary	Python	O(n)	O(d)	Medium	Trie, DFS	AGAIN (not start)
698	Partition to K Equal Sum Subsets	Python	O(n 2^n)*	O(2^n)	Medium	DFS, DP, Memoization, similar as `#416 Partition Equal Subset Sum, #473 Matchsticks to Square`	AGAIN (not start*)
718	Maximum Length of Repeated Subarray	Python	O(m n)*	O(min(m, n))	Medium	DP, Hash, Binary Search	AGAIN (not start*)
784	Letter Case Permutation	Python	O(n 2^n)*	O(1)	Medium	dfs, recursion, `good trick`,`fb`	AGAIN****** (3)
980	Unique Paths III	Python	O(n 2^n)*	O(1)	Hard	backtrack, dfs, amazon, google,`fb`	AGAIN**** (1)

Dynamic Programming

#	Title	Solution	Time	Space	Difficulty	Tag	Status
053	Maximum Subarray	Python	O(n)	O(1)	easy	Curated Top 75, brute force, divied & conquer, `DP`,`dp basic`,`amazon`,`fb`	AGAIN******** (5)
062	Unique Paths	Python	O(m n)*	O(m + n)	Medium	Curated Top 75, `dp`, `basic`, fb, google, apple, amazon, m$	AGAIN**** (2)
063	Unique Paths II	Python	O(m n)*	O(m + n)	Medium	`trick`, check `#062 Unique Paths`, `amazon`	AGAIN*
064	Minimum Path Sum	Python	O(m n)*	O(m + n)	Medium	`DP`, `amazon`	AGAIN*
070	Climbing Stairs	Python	O(logn)	O(1)	Easy	Curated Top 75, Matrix Exponentiation, `DP`, `recursion`, `apple`	OK* (2)
072	Edit Distance	Python	O(logn)	O(1)	Hard	top 100 like, `DP`, `recursion`, `apple`, google, amazon	again (not start)
091	Decode Ways	Python	O(n)	O(1)	Medium	Curated Top 75, `good basic`,`dp`, `M$`, `UBER`, `amazon`,`fb`	AGAIN************ (4)
096	Unique Binary Search Trees	Python	O(n)	O(1)	Medium	dp, Math, fb, amazon	AGAIN* (2) (not start)
120	Triangle	Python	O(m n)*	O(n)	Medium	`amazon`	AGAIN* (not start) (2)
123	Best Time to Buy and Sell Stock III	Python	O(m n)*	O(n)	Hard	`amazon`, uber, apple	AGAIN* (not start) (1)
152	Maximum Product Subarray	Python	O(n)	O(1)	Medium	dp, brute force, Curated Top 75, google, amazon, linkedin	AGAIN***** (1)
198	House Robber	Python	O(n)	O(1)	Easy	Curated Top 75, dp basic,`amazon`	AGAIN*** (2)
213	House Robber II	Python	O(n)	O(1)	Medium	brute force, recursion, dp, Curated Top 75, google, amazon	AGAIN (not start)
221	Maximal Square	Python	O(n^2)	O(n)	Medium	EPI, dp, `amazon`,`fb`	AGAIN** (3) (not start)
256	Paint House	Python	O(n)	O(1)	Medium	🔒	AGAIN (not start)
276	Paint Fence	Python	O(n)	O(1)	Easy	🔒	AGAIN
279	Perfect Squares	Python	O(n sqrt(n))*	O(n)	Medium	dp, bfs, trick, Hash, `google`	AGAIN*
303	Range Sum Query - Immutable	Python	ctor: O(n), lookup: O(1)	O(n)	Easy		OK
304	Range Sum Query 2D - Immutable	Python	ctor: O(m n), lookup: O(1)*	O(m n)*	Medium	`dp`,`trick`,`fb`	AGAIN******* (5)
309	Best Time to Buy and Sell Stock with Cooldown	Python	O(n)	O(1)	Medium		AGAIN (not start)
322	Coin Change	Python	O(n k)*	O(k)	Medium	Curated Top 75, bfs, dfs, dp, grab, google, fb, apple, `amazon`	AGAIN************* (5) (MUST)
351	Android Unlock Patterns	Python	O(9^2 2^9)*	O(9 2^9)*	Medium	🔒 Backtracking, DP, `google`	AGAIN (not start)
357	Count Numbers with Unique Digits	Python	O(n)	O(1)	Medium	Backtracking, Math	AGAIN (not start)
361	Bomb Enemy	Python	O(m n)*	O(m n)*	Medium	🔒 , `google`	AGAIN* (2)
368	Largest Divisible Subset	Python	O(n^2)	O(n)	Medium		AGAIN (not start)
375	Guess Number Higher or Lower II	Python	O(n^2)	O(n^2)	Medium		AGAIN (not start)
377	Combination Sum IV	Python	O(nlogn + n t)*	O(t)	Medium	Curated Top 75, AGAIN, dp basic ,`fb`	AGAIN******** (3)
403	Frog Jump	Python	O(nlogn + n t)*	O(t)	Hard	dfs, bfs, Memoization dfs, dp, amazon, tik-tok, m$	AGAIN (not start)
416	Partition Equal Subset Sum	Python	O(n s)*	O(s)	Medium	dp, fb, google, apple, amazon	AGAIN** (not start) (1)
418	Sentence Screen Fitting	Python	O(r + n c)*	O(n)	Medium	🔒, `dp`, `google`	AGAIN (not start)
467	Unique Substrings in Wraparound String	Python	O(n)	O(1)	Medium		AGAIN (not start)
471	Encode String with Shortest Length	Python	O(n^3) on average	O(n^2)	Medium	🔒, `dp`, `google`	AGAIN (not start)
472	Concatenated Words	Python	O(n l^2)*	O(n l)*	Hard	`good trick`,trie+dfs, `dp`, `dfs`,`amazon`	AGAIN******** (3)
474	Ones and Zeroes	Python	O(s m * n)*	O(m n)*	Medium	`dp`, `google`	AGAIN (not start)
486	Predict the Winner	Python	O(n^2)	O(n)	Medium	`good basic`,`dp`, `google`	AGAIN*****
509	Fibonacci Number	Python	O(logn)	O(1)	Easy	variant of Climbing Stairs, `Matrix Exponentiation`, Spotify	OK**
516	Longest Palindromic Subsequence	Python	O(n^2)	O(n)	Medium	`good DP basic`,`dp`, `UBER`, `amazon`	AGAIN******
562	Longest Line of Consecutive One in Matrix	Python	O(m n)*	O(n)	Medium	🔒, `dp`, `google`	AGAIN (not start)
576	Out of Boundary Paths	Python	O(N m * n)*	O(m n)*	Medium	`dp`, `bfs`	AGAIN (not start)
583	Delete Operation for Two Strings	Python	O(m n)*	O(n)	Medium	`dp`, `google`	AGAIN (not start)
650	2 Keys Keyboard	Python	O(sqrt(n))	O(1)	Medium	`dp`,`dp basic` ,`M$`	AGAIN*
673	Number of Longest Increasing Subsequence	Python	O(n^2)	O(n)	Medium	`dp`,`good trick`, `fb`	AGAIN********** (3)
688	Knight Probability in Chessboard	Python	O(k n^2)*	O(n^2)	Medium	`dp`,`dp basic`,`AGAIN`, `M$`,`Goldman Sachs`, `google`, `fb`, `amazon`	AGAIN********* (5)
712	Minimum ASCII Delete Sum for Two Strings	Python	O(m n)*	O(n)	Medium	`dp`	AGAIN (not start)
714	Best Time to Buy and Sell Stock with Transaction Fee	Python	O(n)	O(1)	Medium	AGAIN, `good basic`, `dp`, `greedy`,`fb`	AGAIN******** (3)
740	Delete and Earn	Python	O(n)	O(1)	Medium		AGAIN (not start)
746	Min Cost Climbing Stairs	Python	O(n)	O(1)	Easy	`good dp basic`,`dp`, `amazon`	AGAIN**** (2)
750	Number Of Corner Rectangles	Python	O(n m^2)*	O(n m)*	Medium	`dp`,`fb`	AGAIN (3) (not start)
764	Largest Plus Sign	Python	O(n^2)	O(n^2)	Medium	`dp`, complex ,`fb`	AGAIN (not start) (2)
788	Rotated Digits	Python	O(logn)	O(logn)	Easy	`Brute Force`, Memoization	OK*
790	Domino and Tromino Tiling	Python	O(logn)	O(1)	Medium	Matrix Exponentiation, `dp`, `google`	AGAIN (not start)
799	Champagne Tower	Python	O(n^2)	O(n)	Medium	`dp`	AGAIN
801	Minimum Swaps To Make Sequences Increasing	Python	O(n)	O(1)	Medium	`dp`, `amazon`, `fb`	AGAIN***** (not start) (2)
808	Soup Servings	Python	O(1)	O(1)	Medium		AGAIN (not start)
813	Largest Sum of Averages	Python	O(k n^2)*	O(n)	Medium	`dp`, `google`	AGAIN (not start)
823	Binary Trees With Factors	Python	O(n^2)	O(n)	Medium	`dp`	AGAIN (not start)
837	New 21 Game	Python	O(n)	O(n)	Medium	`dp`, `google`	AGAIN (not start)
838	Push Dominoes	Python	O(n)	O(n)	Medium	`dp`,`two pointers`,`google`	AGAIN (not start)
877	Stone Game	Python	O(n^2)	O(n)	Medium	variant of Predict the Winner	AGAIN (not start)
926	Flip String to Monotone Increasing	Python	O(n)	O(1)	Medium	good trick, dp, prefix sum, `google`, `amazon`	AGAIN********** (4)
931	Minimum Falling Path Sum	Python	O(n^2)	O(1)	Medium	`google`, `goldman sachs`	AGAIN (not start)
935	Knight Dialer	Python	O(logn)	O(1)	Medium	Matrix Exponentiation, `google`, `M$`, `fb`	AGAIN (not start)
518	Coin Change 2	Python	O(logn)	O(1)	Medium	`dp basic`,`good trick`,check `# 322 Coin Change`,`dp`, `google`, `fb`	AGAIN******** (4)
494	Target Sum	Python	O(logn)	O(1)	Medium	dp basic, `dp`, `fb`	AGAIN***** (1)
1000	Minimum Cost to Merge Stones	Python	O(logn)	O(1)	Medium	dp, amazon	AGAIN (not start)
1143	Longest Common Subsequence	Python	O(logn)	O(1)	Medium	Curated Top 75, Memoization, dp, amazon, karat	AGAIN*** (2) (not start)
1312	Minimum Insertion Steps to Make a String Palindrome	Python	O(logn)	O(1)	Hard	dp, amazon	AGAIN (not start)
1335	Minimum Difficulty of a Job Schedule	Python	O(logn)	O(1)	Medium	`dp`, `amazon`	not start
1799	Maximize Score After N Operations	Python	O(logn)	O(1)	Medium	`dp`, `amazon`	not start

Greedy

#	Title	Solution	Time	Space	Difficulty	Tag, Note	Status
011	Container With Most Water	Python	O(n)	O(1)	Medium	Curated Top 75, good basics, `two pointers`,`fb`, amazon	OK*** (3) (but again !!)
045	Jump Game II	Python	O(n)	O(1)	Medium	Greedy, google, apple, fb, tesla, `amazon`	AGAIN******** (2) (MUST)
055	Jump Game	Python	O(n)	O(1)	Medium	Curated Top 75, good trick, Greedy, DP, `amazon`	AGAIN******** (5)
084	Largest Rectangle in Histogram	Python	O(n)	O(1)	Hard	top 100 like, 2 pointers, brute force, divide and conquer, stack, LC 085, amazon, fb	AGAIN (not start)
122	Best Time to Buy and Sell Stock II	Python	O(n)	O(1)	Easy	compare with `#309 Best Time to Buy and Sell Stock with Cooldown` , `#714 Best Time to Buy and Sell Stock with Transaction Fee`, `amazon`	OK* (2)
134	Gas Station	Python	O(n)	O(1)	Medium	trick, greedy,`amazon`	AGAIN****** (5)
135	Candy	Python	O(n)	O(1)	Hard	LC 123, greedy, array, `amazon`	AGAIN (not start)
330	Patching Array	Python	O(n)	O(1)	Hard	array, greedy,`amazon`	AGAIN (not start)
358	Rearrange String k Distance Apart	Python	O(n)	O(1)	Medium	heap, greedy, check LC 767	not start
376	Wiggle Subsequence	Python	O(n)	O(1)	Medium		AGAIN*
392	Is Subsequence	Python	O(n)	O(1)	Medium	`basics`	OK*
397	Integer Replacement	Python	O(n)	O(1)	Medium	`Recursion basics`, Math	OK*
402	Remove K Digits	Python	O(n)	O(n)	Medium	LintCode	AGAIN (not start*)
435	Non-overlapping Intervals	Python	O(nlogn)	O(1)	Medium	Curated Top 75, good trick, 2 pointers, inverval, similiar as `#452 Minimum Number of Arrows to Burst Balloons`, Line Sweep, `google`	AGAIN********* (6)
452	Minimum Number of Arrows to Burst Balloons	Python	O(nlogn)	O(1)	Medium		AGAIN*
455	Assign Cookies	Python	O(nlogn)	O(1)	Easy		OK*
621	Task Scheduler	Python	O(n)	O(1)	Medium	`trick`,`array`,`greedy`, `fb`, `amazon`	AGAIN****** (7)
646	Maximum Length of Pair Chain	Python	O(nlogn)	O(1)	Medium	good trick, greedy, similar as `#435 Non-overlapping Intervals`, Line Sweep, `amazon`	OK********** (5) (but again)
649	Dota2 Senate	Python	O(n)	O(n)	Medium	complex question	AGAIN (not start*)
659	Split Array into Consecutive Subsequences	Python	O(n)	O(1)	Medium		AGAIN (not start*)
738	Monotone Increasing Digits	Python	O(1)	O(1)	Medium	good trick, greedy, string, trick, `Amazon`	AGAIN********* (4)
763	Partition Labels	Python	O(n)	O(n)	Medium	greedy,trick,dict,index,`amazon`	AGAIN******* (5) (AGAIN)
767	Reorganize String	Python	O(n)	O(1)	Medium	`greedy`,`counter`,`good trick`,`amazon`,`fb`	AGAIN**************** (7) (MUST)
861	Score After Flipping Matrix	Python	O(r c)*	O(1)	Medium		AGAIN (not start*)
870	Advantage Shuffle	Python	O(nlogn)	O(n)	Medium		OK*
881	Boats to Save People	Python	O(nlogn)	O(n)	Medium	`good trick`	OK*
948	Bag of Tokens	Python	O(nlogn)	O(1)	Medium	Two Pointers	AGAIN (not start)
962	Maximum Width Ramp	Python	O(n)	O(n)	Medium	Descending Stack	AGAIN (not start)
1024	Video Stitching	Python			Medium	Spotify	AGAIN (not start)
1102	Path With Maximum Minimum Value	Python			Medium	dfs, dp , greedy, `amazon`	not start
319	Bulb Switcher	Python			Medium		not start
672	Bulb Switcher II	Python			Medium		not start
1375	Bulb Switcher III	Python			Medium	queue, array, `gra*`	AGAIN*** (1)
1648	Sell Diminishing-Valued Colored Balls	Python			Medium	trick, sorting, heapq, binary search, greedy, `amazon`	AGAIN*** (2) (not start)
1710	Maximum Units on a Truck	Python			Easy	sort, greedy, `amazon`	AGAIN******** (3) (MUST)

Graph

#	Title	Solution	Time	Space	Difficulty	Status	Note
269	Alien Dictionary	Python			Hard	Curated Top 75, dfs, bfs, topology sort, `fb`, google, m$, airbnb, uber, amazon	AGAIN******** (3) (not start)
323	Number of Connected Components in an Undirected Graph	Python	O(n)	O(n)	Medium	Curated Top 75, 🔒 , dfs, Union Find, `graph`, `linkedin`, `amazon`, fb, google, m$, linkedin	AGAIN************** (5) (MUST)
959	Regions Cut By Slashes	Python	O(n^2)	O(n^2)	Medium	Union Find
1135	Connecting Cities With Minimum Cost	Python	O(n^2)	O(n^2)	Medium	union find, Kruskal, prime, graph, amazon	AGAIN (not start)

Geometry

#	Title	Solution	Time	Space	Difficulty	Note
892	Surface Area of 3D Shapes	C++ Python	O(n^2)	O(1)	Easy
0587	Erect the Fence	Python	O(nlogn)	O(n)	Hard	complex, Convex Hull, `Monotone Chain` , `amazon`
0892	Surface Area of 3D Shapes

Design

#	Title	Solution	Time	Space	Difficulty	Tag	Note
0146	LRU Cache	Python	O(1)	O(k)	Hard	good basic, LRU,Least Recently Used, LinkedHashMap, OrderedDict, priority queue, LinkedList, `amazon`	AGAIN***** (3)
0225	Implement Stack using Queues	C++ Python	push: O(n), pop: O(1), top: O(1)	O(n)	Easy
284	Peeking Iterator	C++ Python	O(1)	O(1)	Medium	good basic, `google`, apple	not start*** (1)
348	Design Tic-Tac-Toe	Python	O(1)	O(n^2)	Medium	matrix, array, 🔒, google, `fb`, `amazon`	AGAIN****** (5)
353	Design Snake Game	C++ Python	O(1)	O(s)	Medium	🔒, amazon, google, square, m$	Deque
355	Design Twitter	Python	O(klogu)	O(t + f)	Medium	good trick, data structure, heapq, defaultdict, `amazon`	OK******** (6)
0359	Logger Rate Limiter	C++ Python	O(1), amortized	O(k)	Easy	🔒	Deque
0362	Design Hit Counter	C++ Python	O(1), amortized	O(k)	Medium	🔒	Deque
0379	Design Phone Directory	C++ Python	O(1)	O(n)	Medium	🔒
0380	Insert Delete GetRandom O(1)	Python	O(1)	O(n)	Medium/Hard	set, list, dict, `amazon`,`fb`	OK* (5)
0381	Insert Delete GetRandom O(1) - Duplicates allowed	C++ Python	O(1)	O(n)	Hard
432	All O`one Data Structure	C++ Python	O(1)	O(n)	Hard
460	LFU Cache	Python	O(1)	O(k)	Hard	Least Frequently Used (LFU) cache, complex, `amazon`	AGAIN*** (2) (not start)
535	Encode and Decode TinyURL	Python	O(1)	O(n)	Medium	`hash map`, "duplicated", "hash map collision" ,`UBER`, `amazon`,`google` ,`fb`, design	OK**** (5)
588	Design In-Memory File System	C++ Python	ls: O(l + klogk) mkdir: O(l) addContentToFile: O(l + c) readContentFromFile: O(l + c)	O(n + s)	Hard	dict, a bit complex basic, 🔒, shoptify, amazon	AGAIN******* (3)
0604	Design Compressed String Iterator	C++ Python	O(1)	O(1)	Easy	🔒
622	Design Circular qeque	Python			Medium	🔒
631	Design Excel Sum Formula	C++ Python	set: O((r c)^2)* get: O(1) sum: O((r c)^2)*	O(r c)*	Hard	🔒
635	Design Log Storage System	C++ Python	put: O(1) retrieve: O(n + dlogd)	O(n)	Medium	🔒
641	Design Circular Deque	Python			Medium	🔒
642	Design Search Autocomplete System	Python	O(p^2)	O(p t + s)*	Hard	🔒, `amazon`	AGAIN**** (not start) (5)
705	Design HashSet	Python			Easy
706	Design HashMap	Python			Easy
0715	Range Module	C++ Python	add: O(n) remove: O(n) query: O(logn)	O(n)	Hard
716	Max Stack	Python	push: O(logn) pop: O(logn) popMax: O(logn) top: O(1) peekMax: O(1)	O(n)	Easy	basic, stack, `amazon`	again*
745	Prefix and Suffix Search	Python	ctor: O(w l^2)* search : O(p + s)	O(t)	Hard	Trie, `fb`	Not start* (1) (good basic)
900	RLE Iterator	C++ Python	O(n)	O(1)	Medium
1146	Snapshot Array	C++ Python	set: O(1) get: O(logn)	O(n)	Medium
1166	Design File System	C++ Python	create: O(n) get: O(n)	O(n)	Medium	🔒, design, google, airbnb, amazon	AGAIN***** (1)
1172	Dinner Plate Stacks	C++ Python	push: O(logn) pop: O(1), amortized popAtStack: (logn)	O(n c)*	Hard
1206	Design Skiplist	C++ Python	O(logn), on average	O(n)	Hard
1236	Web Crawler	C++ Python	O(\|V\| + \|E\|)	O(\|V\|)	Medium	🔒, BFS, DFS
1244	Design A Leaderboard	C++ Python	ctor: O(1) add: O(1) top: O(n) reset: O(1)	O(n)	Medium
1268	Search Suggestions System	Python	ctor: O(n l)* suggest: O(l^2)	O(t)	Medium	good basic, array, heap, sort, Trie, `amazon`	AGAIN******** (3)
1286	Iterator for Combination	C++ Python	O(k)	O(k)	Medium	Stack
1429	First Unique Number	Python	O(k)	O(k)	Medium	good trick, heap, `amazon`	AGAIN*** (not start)
1472	Design Browser History	Python	O(k)	O(k)	Medium		AGAIN
1500	Design a File Sharing System	Python	O(k)	O(k)	Medium	design, hashmap	AGAIN*** (not start)
1603	Design Parking System	Python	O(k)	O(k)	Easy	design, amazon , paypal	OK
1628	Design an Expression Tree With Evaluate Function	Python	O(k)	O(k)	Medium	complex, design, `amazon`	AGAIN*** (not start)
1656	Design an Ordered Stream	Python	O(k)	O(k)	Easy
1670	Design Front Middle Back Queue	Python	O(k)	O(k)	Medium	good basic, Design, `amazon`	AGAIN** (1) (not start)
1756	Design Recent Used Queue	Python	O(k)	O(k)	Medium	design, queue	AGAIN
1797	Design Authentication Manager	Python	O(k)	O(k)	Medium	design, hashmap	AGAIN
1976	Number of Ways to Arrive at Destination	Python	O(k)	O(k)	Medium

Simulation

#	Title	Solution	Time	Space	Difficulty	Status	Note
874	Walking Robot Simulation	C++ Python	O(n + k)	O(k)	Easy

Concurrency

#	Title	Solution	Time	Space	Difficulty	Tag
1114	Print in Order	C++ Python	O(n)	O(1)	Easy
1115	Print FooBar Alternately	C++ Python	O(n)	O(1)	Medium
1116	Print Zero Even Odd	C++ Python	O(n)	O(1)	Medium
1117	Building H2O	C++ Python	O(n)	O(1)	Hard
1188	Design Bounded Blocking Queue	C++ Python	O(n)	O(1)	Medium	🔒
1195	Fizz Buzz Multithreaded	C++ Python	O(n)	O(1)	Medium
1226	The Dining Philosophers	C++ Python	O(n)	O(1)	Medium
1242	Web Crawler Multithreaded	C++ Python	O(\|V\| + \|E\|)	O(\|V\|)	Medium	🔒
1279	Traffic Light Controlled Intersection	C++ Python	O(n)	O(1)	Easy	🔒

SQL

#	Title	Solution	Time	Space	Difficulty	Tag, Note	Status
0175	Combine Two Tables	MySQL	O(m + n)	O(m + n)	Easy		OK (4)
0176	Second Highest Salary	MySQL	O(n)	O(1)	Easy	`amazon`,`fb`	OK (4)
0177	Nth Highest Salary	MySQL	O(n^2)	O(n)	Medium	`MySQL PROCEDURE`, `SQL FAQ`	AGAIN*** (3)
0178	Rank Scores	MySQL	O(n^2)	O(n)	Medium	`trick`, `SQL var`, ank, select same table, rank	AGAIN****** (7)
0180	Consecutive Numbers	MySQL	O(n)	O(n)	Medium	`SQL var`, join same table multi times	OK* (3)
0181	Employees Earning More Than Their Managers	MySQL	O(n^2)	O(1)	Easy		OK
0182	Duplicate Emails	MySQL	O(n^2)	O(n)	Easy		OK
0183	Customers Who Never Order	MySQL	O(n^2)	O(1)	Easy	left join	OK** (3) (but again)
0184	Department Highest Salary	MySQL	O(n^2)	O(n)	Medium	`trick`, where, good basic	OK***** (but again) (6)
0185	Department Top Three Salaries	MySQL	O(n^2)	O(n)	Hard	similiar as `# 0177 Nth Highest Salary`, good trick, top N in group	AGAIN******** (5)
0196	Delete Duplicate Emails	MySQL	O(n^2)	O(n)	Easy, delete command		AGAIN (2)
0197	Rising Temperature	MySQL	O(n^2)	O(n)	Easy		OK
0262	Trips and Users	MySQL	O((t u) + tlogt)*	O(t)	Hard	case condisions	OK* (2)
0511	Game Play Analysis I	MySQL	O(n)	O(n)	Easy	🔒	OK
0512	Game Play Analysis II	MySQL	O(n)	O(n)	Easy	🔒, `2 col where` `good trick`	AGAIN**(4)
0534	Game Play Analysis III	MySQL	O(nlogn)	O(n)	Medium	🔒, `SQL var`, `tricky`, window func	AGAIN******** (6)
0550	Game Play Analysis IV	MySQL	O(n)	O(n)	Medium	case, fraction, join, good basic, where min condition	OK*********** (7) (but again)
569	Median Employee Salary	MySQL	O(n)	O(n)	Medium	medium number	AGAIN* (not start)
571	Find Median Given Frequency of Numbers	MySQL	O(n)	O(n)	Medium	medium number	AGAIN** (not start) (2)
577	Employee Bonus	MySQL	O(n)	O(n)	Easy		OK
578	Get Highest Answer Rate Question	MySQL			Medium	`fb`, case condition	OK* (3)
579	Find Cumulative Salary of an Employee	MySQL			Hard	window function, `amazon`, good trick	OK***** (5)(but again)
580	Count Student Number in Departments	MySQL			Medium		OK*** (2) (but again)
595	Big Countries	MySQL			Easy		OK
597	Friend Requests I: Overall Acceptance Rate	MySQL			Medium	select distinct, ifnull,`fb`	OK*** (7)
601	Human Traffic of Stadium	MySQL			Hard	consecutive nums	OK* (1)
602	Friend Requests II: Who Has Most Friend?	MySQL			Medium	union all, `fb`	OK*** (4)
603	Consecutive Available Seats	MySQL			Medium	consecutive nums, good basic, cross join	OK***** (3)(but again)
618	Students Report By Geography	MySQL			Hard	sql var	AGAIN (not start)
620	Not Boring Movies	MySQL			Easy		OK
626	Exchange Seats	MySQL			Medium		AGAIN (not start)
627	Swap Salary	MySQL			Easy	UPDATE with CASE, good basic	OK* (1) (but again)
1045	Customers Who Bought All Products	MySQL	O(n + k)	O(n + k)	Medium	🔒, where with count	OK*** (4)
1050	Actors and Directors Who Cooperated At Least Three Times	MySQL	O(n)	O(n)	Easy	🔒	OK
1068	Product Sales Analysis I	MySQL	O(m + n)	O(m + n)	Easy	🔒	OK
1069	Product Sales Analysis II	MySQL	O(n)	O(n)	Easy	🔒	OK
1070	Product Sales Analysis III	MySQL	O(n)	O(n)	Medium	🔒	OK
1075	Project Employees I	MySQL	O(m + n)	O(m + n)	Easy	🔒	OK
1076	Project Employees II	MySQL	O(n)	O(n)	Easy	🔒	OK (2)
1077	Project Employees III	MySQL	O((m + n)^2)	O(m + n)	Medium	🔒, `tricky where`	OK***** (2) (but again)
1082	Sales Analysis I	MySQL	O(n)	O(n)	Easy	🔒, group by only 1 col, good basic	OK***** (5) (again)
1083	Sales Analysis II	MySQL	O(m + n)	O(m + n)	Easy	🔒, not in	OK*** (3) (again)
1084	Sales Analysis III	MySQL	O(m + n)	O(m + n)	Easy	🔒	OK** (2)
1097	Game Play Analysis V	MySQL	O(n^2)	O(n)	Hard	🔒, `good basic`,`retention`, case condition, retention, data_add, left join	AGAIN******* (8)
1098	Unpopular Books	MySQL	O(m + n)	O(n)	Medium	🔒, where not in	OK* (2)
1107	New Users Daily Count	MySQL	O(n)	O(n)	Medium	🔒	OK*
1112	Highest Grade For Each Student	MySQL	O(nlogn)	O(n)	Medium	🔒, good basic	OK** (4)
1113	Reported Posts	MySQL	O(n)	O(n)	Easy	🔒	OK
1126	Active Businesses	MySQL	O(n)	O(n)	Medium	🔒, `good basic`	AGAIN*** (3)
1127	User Purchase Platform	MySQL	O(n)	O(n)	Hard	🔒, `complex`, union all, case	OK**** (6) (but again)
1132	Reported Posts II	MySQL	O(m + n)	O(n)	Medium	🔒	OK*** (4)
1141	User Activity for the Past 30 Days I	MySQL	O(n)	O(n)	Easy	🔒	AGAIN* (2)
1142	User Activity for the Past 30 Days II	MySQL	O(n)	O(n)	Easy	🔒	AGAIN* (1)
1148	Article Views I	MySQL	O(nlogn)	O(n)	Easy	🔒	OK
1149	Article Views II	MySQL	O(nlogn)	O(n)	Medium	🔒	OK*
1158	Market Analysis I	MySQL	O(m + n)	O(m + n)	Medium	🔒, `case when ... is not null`	AGAIN**** (5)
1159	Market Analysis II	MySQL	O(m + n)	O(m + n)	Hard	🔒, good trick	AGAIN** (3)
1164	Product Price at a Given Date	MySQL	O(mlogn)	O(m)	Medium	🔒, good trick, union, case, not in a period	AGAIN******** (2)
1173	Immediate Food Delivery I	MySQL	O(n)	O(1)	Easy	🔒	OK
1174	Immediate Food Delivery II	MySQL	O(n)	O(m)	Medium	🔒	OK**** (3)
1179	Reformat Department Table	MySQL	O(n)	O(n)	Easy	🔒	OK
1193	Monthly Transactions I	MySQL	O(n)	O(n)	Medium	🔒	OK (2)
1194	Tournament Winners	MySQL	O(m + n + nlogn)	O(m + n)	Hard	🔒	AGAIN*
1204	Last Person to Fit in the Elevator	MySQL	O(nlogn)	O(n)	Medium	🔒, cumsum, window func, good basic	OK****** (3)
1205	Monthly Transactions II	MySQL	O(n)	O(n)	Medium	🔒, good trick, union all, case conditions	OK*** (3) (but again)
1211	Queries Quality and Percentage	MySQL	O(n)	O(n)	Easy		OK
1212	Team Scores in Football Tournament	MySQL	O(nlogn)	O(n)	Medium	good trick	OK** (2)
1225	Report Contiguous Dates	MySQL	O(nlogn)	O(n)	Hard	🔒	AGAIN* (2) (not start)
1241	Number of Comments per Post	MySQL	O(n)	O(n)	Easy	🔒, good basic	OK**** (5) (but again)
1251	Average Selling Price	MySQL	O(n)	O(n)	Easy	🔒, good basic	OK*** (but again) (3)
1264	Page Recommendations	MySQL	O(m + n)	O(m)	Medium	🔒	OK** (2)
1270	All People Report to the Given Manager	MySQL	O(n)	O(n)	Medium	🔒, good basic	OK* (3)
1280	Students and Examinations	MySQL	O((m n) * log(m * n))*	O(m n)*	Easy	🔒	OK (1)
1285	Find the Start and End Number of Continuous Ranges	MySQL	O(n)	O(n)	Medium	🔒, variable	AGAIN (not start) (1)
1294	Weather Type in Each Country	MySQL	O(m + n)	O(n)	Easy	🔒	OK (1)
1303	Find the Team Size	MySQL	O(n)	O(n)	Easy	🔒	ok (1)
1308	Running Total for Different Genders	MySQL	O(nlogn)	O(n)	Medium	🔒, good basic, union all, window func	OK**** (3)
1321	Restaurant Growth	MySQL	O(n^2)	O(n)	Medium	🔒, good basic, trick	AGAIN***** (3)
1322	Ads Performance	MySQL	O(nlogn)	O(n)	Easy	🔒, good basic	OK******* (3) (but again)
1327	List the Products Ordered in a Period	MySQL	O(n)	O(n)	Easy	🔒	OK
1336	Number of Transactions per Visit	MySQL	O(m + n)	O(m + n)	Medium	🔒, complex, variable	AGAIN (not start)
1341	Movie Rating	MySQL	O(nlogn)	O(n)	Medium	🔒	AGAIN (not start)
1350	Students With Invalid Departments	MySQL	O(n)	O(n)	Easy	🔒	OK
1355	Activity Participants	MySQL	O(n)	O(n)	Medium	🔒	OK
1364	Number of Trusted Contacts of a Customer	MySQL	O(n + m + l + nlogn)	O(n + m + l)	Medium	🔒	OK
1369	Get the Second Most Recent Activity	MySQL	O(nlogn)	O(n)	Hard	🔒, union, having	OK** (2) (but again)
1378	Replace Employee ID With The Unique Identifier	MySQL	O(n)	O(n)	Easy	🔒	OK
1384	Total Sales Amount by Year	MySQL	O(nlogn)	O(n)	Hard	🔒, complex	OK*
1393	Capital Gain/Loss	MySQL	O(n)	O(n)	Medium	🔒	OK
1398	Customers Who Bought Products A and B but Not C	MySQL	O(m + n)	O(m + n)	Medium	🔒	OK
1407	Top Travellers	MySQL	O(m + nlogn)	O(m + n)	Easy	🔒, ifnull	OK*
1412	Find the Quiet Students in All Exams	MySQL	O(m + nlogn)	O(m + n)	Hard	🔒, good trick, not in, inner join on multiple cols	OK**** (3) (but again)
1421	NPV Queries	MySQL	O(n)	O(n)	Medium	🔒	OK
1435	Create a Session Bar Chart	MySQL	O(n)	O(1)	Easy	🔒	OK
1440	Evaluate Boolean Expression	MySQL	O(n)	O(n)	Medium	🔒	OK
1445	Apples & Oranges	MySQL	O(n)	O(n)	Medium	🔒	OK
1454	Active Users	MySQL	O(nlogn)	O(n)	Medium	🔒, good basic, window func	AGAIN*** (2)
1459	Rectangles Area	MySQL	O(n^2)	O(n^2)	Medium	🔒	OK*
1468	Calculate Salaries	MySQL	O(m + n)	O(m + n)	Easy	🔒	OK*
1479	Sales by Day of the Week	MySQL	O(m + n)	O(n)	Hard	🔒, case, DAYOFWEEK	OK
1484	Group Sold Products By The Date	MySQL	O(nlogn)	O(n)	Easy	🔒, `GROUP_CONCAT`	OK*
1495	Friendly Movies Streamed Last Month	MySQL	O(n)	O(n)	Easy	🔒	OK
1501	Countries You Can Safely Invest In	MySQL	O(n)	O(n)	Medium	🔒,good trick, group avg, global avg, SUBSTRING, inner join on `or conditions`	OK****** (4)
1511	Customer Order Frequency	MySQL	O(n)	O(n)	Easy	🔒, having, like	OK* (1)
1517	Find Users With Valid E-Mails	MySQL	O(n)	O(n)	Easy	🔒, regular expression	AGAIN
1527	Patients With a Condition	MySQL	O(n)	O(n)	Easy	🔒	OK
1532	The Most Recent Three Orders	MySQL	O(nlogn)	O(n)	Medium	🔒, window func, good basic	OK** (2) (but again)
1543	Fix Product Name Format	MySQL	O(nlogn)	O(n)	Easy	🔒, trim	OK
1549	The Most Recent Orders for Each Product	MySQL	O(nlogn)	O(n)	Medium	🔒, max day per id, good basic	OK* (again)
1555	Bank Account Summary	MySQL	O(m + n)	O(m + n)	Medium	🔒, union all, good trick	OK**** (2)(but again)
1565	Unique Orders and Customers Per Month	MySQL	O(n)	O(n)	Easy	🔒	OK
1571	Warehouse Manager	MySQL	O(n)	O(n)	Medium	🔒	OK* (1)
1581	Customer Who Visited but Did Not Make Any Transactions	MySQL	O(n)	O(n)	Easy	🔒, left join, good basic	OK** (2)(but again)
1587	Bank Account Summary II	MySQL	O(m + n)	O(m + n)	Easy	🔒	OK
1596	The Most Frequently Ordered Products for Each Customer	MySQL	O(n)	O(n)	Medium	🔒, good trick, `rank() ORDER BY count`, get max in each group	OK********* (3)(but again)
1607	Sellers With No Sales	MySQL	O(nlogm)	O(n + m)	Medium	🔒	OK
1613	Find the Missing IDs	MySQL	O(n^2)	O(n)	Medium	🔒, `RECURSIVE CTE`, good trick	AGAIN*** (2)
1623	All Valid Triplets That Can Represent a Country	MySQL	O(n^3)	O(n^3)	Easy	🔒, `<>`	AGAIN* (not start)
1633	Percentage of Users Attended a Contest	MySQL	O(m + nlogn)	O(n)	Easy	🔒	OK
1635	Hopper Company Queries I	MySQL	O(d + r + tlogt)	O(d + r + t)	Hard	🔒, complex	AGAIN (not start)
1645	Hopper Company Queries II	MySQL	O(d + r + tlogt)	O(d + r + t)	Hard	🔒, complex	AGAIN (not start)
1651	Hopper Company Queries III	MySQL	O(d + r + tlogt)	O(d + r + t)	Hard	🔒, complex	AGAIN (not start)
1661	Average Time of Process per Machine	MySQL	O(n)	O(n)	Easy	🔒, good basic	OK* (1)
1667	Fix Names in a Table	MySQL	O(nlogn)	O(n)	Easy	🔒, concat, sub-string	OK (1)
1677	Product's Worth Over Invoices	MySQL	O(nlogn)	O(n)	Easy	🔒	OK
1683	Invalid Tweets	MySQL	O(n)	O(n)	Easy	🔒	OK
1693	Daily Leads and Partners	MySQL	O(n)	O(n)	Easy	🔒	OK
1699	Number of Calls Between Two Persons	MySQL	O(n)	O(n)	Medium	🔒, cte, union all	OK* (1)(but again)
1709	Biggest Window Between Visits	MySQL	O(nlogn)	O(n)	Medium	🔒, window func, datediff, coalesce, good trick	AGAIN***** (2)
1715	Count Apples and Oranges	MySQL	O(n)	O(n)	Medium	🔒, ifnull	OK (2)
1729	Find Followers Count	MySQL	O(nlogn)	O(n)	Easy	🔒	OK
1731	The Number of Employees Which Report to Each Employee	MySQL	O(nlogn)	O(n)	Easy	🔒	OK
1741	Find Total Time Spent by Each Employee	MySQL	O(nlogn)	O(n)	Easy	🔒	OK
1747	Leetflex Banned Accounts	MySQL	O(n^2)	O(n)	Medium	🔒	OK (2) (but again)
1757	Recyclable and Low Fat Products	MySQL	O(n)	O(n)	Easy	🔒	OK
1767	Find the Subtasks That Did Not Execute	MySQL	O(n c)*	O(n c)*	Hard	🔒, `RECURSIVE CTE`	AGAIN (not start)
1777	Product's Price for Each Store	MySQL	O(n)	O(n)	Easy	🔒	OK (2)
1783	Grand Slam Titles	MySQL	O(n)	O(n)	Medium	🔒, union all, good basic	OK* (1) (but again)
1789	Primary Department for Each Employee	MySQL	O(n)	O(n)	Easy	🔒, where id in	OK (1) (but again)
1795	Rearrange Products Table	MySQL	O(n)	O(n)	Easy	🔒, union all, good basic	OK****** (2)
1809	Ad-Free Sessions	MySQL	O(n)	O(n)	Easy	🔒, left join where col is null	OK**** (3)(but again)
1811	Find Interview Candidates	MySQL	O(nlogn)	O(n)	Medium	🔒, union all, cte, where, `good basic`	AGAIN* (2)
1821	Find Customers With Positive Revenue this Year	MySQL	O(n)	O(n)	Easy	🔒	OK
1831	Maximum Transaction Each Day	MySQL	O(nlogn)	O(n)	Medium	🔒, rank(), where on 2 attr, good basic	AGAIN**** (2)
1841	League Statistics	MySQL	O(nlogn)	O(n)	Medium	🔒, case, complex	AGAIN* (2)
1843	Suspicious Bank Accounts	MySQL	O(nlogn)	O(n)	Medium	🔒, good trick, window func	OK** (2) (but AGAIN)
1853	Convert Date Format	MySQL	O(n)	O(n)	Easy	🔒	OK
1867	Orders With Maximum Quantity Above Average	MySQL	O(n)	O(n)	Easy	🔒	OK (1)
1873	Calculate Special Bonus	MySQL	O(n)	O(n)	Easy	🔒, left, odd num	OK (2)
1875	Group Employees of the Same Salary	MySQL	O(nlogn)	O(n)	Medium	🔒, complex, good basic	AGAIN* (1)
1890	The Latest Login in 2020	MySQL	O(n)	O(n)	Easy	🔒	OK
1892	Page Recommendations II	MySQL	O(n m)*	O(n m)* Hard	🔒	AGAIN*** (1) (not start)
1907	Count Salary Categories	MySQL	O(n)	O(n)	Medium	🔒, union all	OK* (1)
1917	Leetcodify Friends Recommendations	MySQL	O(n^2)	O(n^2)	Hard	🔒, `NOT EXISTS`	AGAIN*** (2)
1919	Leetcodify Similar Friends	MySQL	O(n l)*	O(n l)*	Hard	🔒	AGAIN* (not start)
1934	Confirmation Rate	MySQL	O(n + m)	O(n + m)	Medium	🔒, good basic	OK* (1) (but again)
1939	Users That Actively Request Confirmation Messages	MySQL	O(nlogn)	O(n)	Easy	🔒, TIMESTAMPDIFF, good basic	OK*** (2) (but again)
1949	Strong Friendship	MySQL	O(n^3)	O(n^2)	Medium	🔒	good basic, where in 2 cols
1951	All the Pairs With the Maximum Number of Common Followers	MySQL	O(n^3)	O(n^2)	Medium	🔒, good trick	AGAIN* (2)
1965	Employees With Missing Information	MySQL	O(nlogn)	O(n)	Easy	🔒, good basic	OK* (1) (but again)
1972	First and Last Call On the Same Day	MySQL	O(n)	O(n)	Hard	🔒, rank, union all, amazon	AGAIN** (2)
1978	Employees Whose Manager Left the Company	MySQL	O(nlogn)	O(n)	Easy	🔒	OK (1)
1988	Find Cutoff Score for Each School	MySQL	O(n m)*	O(n m)*	Medium	🔒, no ref	AGAIN (not start)
1990	Count the Number of Experiments	MySQL	O(n)	O(n)	Easy	🔒, cross join	AGAIN* (1)
2004	The Number of Seniors and Juniors to Join the Company	MySQL	O(nlogn)	O(n)	Hard	🔒, not ref	AGAIN (not start)

Shell Script

#	Title	Solution	Time	Space	Difficulty
0192	Word Frequency	Shell	O(n)	O(k)	Medium
0193	Valid Phone Numbers	Shell	O(n)	O(1)	Easy
0194	Transpose File	Shell	O(n^2)	O(n^2)	Medium
0195	Tenth Line	Shell	O(n)	O(1)	Easy

Cheap and reliable Node.js hosting starts at $3/month, and $1/month static HTML hosting

yennanliu / CS_basics

Programming Languages

Labels

Projects that are alternatives of or similar to CS basics

CS_BASICS

pic_source

Resource

Algorithms content

Database

Shell

Progress

Data Structure

Algorithm

Array

Hash Table

Linked list

Stack

Tree

Heap

Bit Manipulation

String

Queue

Math

Sort

Two Pointers

Recursion

Binary Search

Binary Search Tree

Breadth-First Search

Depth-First Search

Backtracking

Dynamic Programming

Greedy

Graph

Geometry

Design

Simulation

Concurrency

SQL

Shell Script