Must Do Coding Questions in Java

Array

S.No	Question Link	Solution	Difficulty
1	Subarray with given sum	Subarray with given sum	Easy
2	Kadane's Algorithm	Kadane's Algorithm	Medium
3	Missing number in array	Missing number in array	Easy
4	Merge Without Extra Space	Merge Without Extra Space	Hard
5	Rearrange Array Alternately	Rearrange Array Alternately	Medium
6	Largest Number formed from an Array	Largest Number formed from an Array	Medium
7	Spirally traversing a matrix	Spirally traversing a matrix	Easy
8	Convert array into Zig-Zag fashion	Convert array into Zig-Zag fashion	Easy
9	Trapping Rain Water	Trapping Rain Water	Medium
10	Kth smallest element	Kth smallest element	Medium
11	Reverse array in groups	Reverse array in groups	Basic
12	Minimum Platforms	Minimum Platforms	Medium
13	Leaders in an array	Leaders in an array	Easy
14	Equilibrium Point	Equilibrium Point	Easy
15	Reverse Array	Reverse array	Easy
16	Sort 0 1 2	Sort 0 1 2	Easy
17	Remove Duplicates from Sorted Array	Remove Duplicates from Sorted Array	Easy
18	Rotate Array	Rotate Array	Easy
19	Maximum of all subarrays of size k	Maximum of all subarrays of size k	Medium
20	Single Number	Single Number	Easy
21	Intersection of Two Arrays II	Intersection of Two Arrays II	Easy
22	Count Triplets	Count Triplets	Medium
23	Help Classmates	Help Classmates	Medium
24	Maximum Product Subarray	Maximum Product Subarray	Medium
25	Reshape the Matrix	Reshape the Matrix	Easy
26	Valid Sudoku	Valid Sudoku	Easy
27	Subarrays with equal 1s and 0s	Subarrays with equal 1s and 0s	Medium
28	First non-repeating character in a stream	First non-repeating character in a stream	Easy
29	First negative integer in every window of size k	First negative integer in every window of size k	Easy
29	Valid Substring	Valid Substring	Easy
30	The Celebrity Problem	The Celebrity Problem	Medium
31	Median of Two Sorted Arrays	Median of Two Sorted Arrays	Medium
32	Maximum Rectangular Area in a Histogram	Maximum Rectangular Area in a Histogram	Medium
33	Count pairs in array divisible by K	Count pairs in array divisible by K	Medium

Searching Algo

S.No	Question Link	Solution	Difficulty
1	Linear Search	Linear Search	Basic
2	Binary Search	Binary Search	Basic
3	First Bad Version	First Bad Version	Easy
4	Search Insert Position	Search Insert Position	Easy
5	Search in Rotated Sorted Array	Search in Rotated Sorted Array	Medium
6	Find Missing And Repeating	Find Missing And Repeating	Medium
7	Majority Element	Majority Element	Medium
8	Searching in an array where adjacent differ by at most k	Searching in an array where adjacent differ by at most k	Medium
9	Find Pair Given Difference	Find Pair Given Difference	Easy
10	Zero Sum Subarrays	Zero Sum Subarrays	Medium

Sorting Algo

S.No	Question Link	Solution	Difficulty
1	Bubble Sort	Bubble Sort	Basic
2	Selection Sort	Selection Sort	Basic
3	Insertion Sort	Insertion Sort	Easy
4	Merge Sort	Merge Sort	Easy

Martix

S.No	Question Link	Solution	Difficulty
1	Spirally traversing a matrix	Spirally traversing a matrix	Medium
2	Search a 2D Matrix	Search a 2D Matrix	Medium
3	Row with max 1s	Row with max 1s	Medium
4	Sorted matrix	Sorted matrix	Basic
5	Maximal Square	Maximal Square	Medium
6	Rotate Image	Rotate Image	Medium
7	Common Elements Present In All Rows Of Matrix	Common Elements Present In All Rows Of Matrix	Medium
8	Solve the Sudoku	Solve the Sudoku	Medium

String

S.No	Question Link	Solution	Difficulty
1	Longest Common Prefix in an Array	Longest Common Prefix in an Array	Medium
2	Reverse words in a given string	Reverse words in a given string	Easy
3	Permutations of a given string	Permutations of a given string	Basic
4	Longest Palindrome in a String	Longest Palindrome in a String	Medium
5	Roman Number to Integer	Roman Number to Integer	Easy
6	Convert to Roman No	Convert to Roman No r	Easy
7	Anagram	Anagram	Easy
8	Longest Substring Without Repeating Characters	Longest Substring Without Repeating Characters	Medium
9	First Unique Character in a String	First Unique Character in a String	Medium
10	Search Pattern	Search Pattern	Medium

LinkedList

S.No	Question Link	Solution	Difficulty
1	Finding middle element in a linked list	Finding middle element in a linked list	Basic
2	Reverse a linked list	Reverse a linked list	Easy
3	Rotate a Linked List	Rotate a Linked List	Easy
4	Reverse a Linked List in groups of given size	Reverse a Linked List in groups of given size	Medium
5	Intersection Point in Y Shapped Linked Lists	Intersection Point in Y Shapped Linked Lists	Medium
6	Detect Loop in linked list	Detect Loop in linked list	Easy
7	Nth node from end of linked list	Nth node from end of linked list	Easy
8	Merge two sorted linked lists	Merge two sorted linked lists	Easy
9	Add two numbers represented by linked lists	Add two numbers represented by linked lists	Easy
10	Check if Linked List is Palindrome	Check if Linked List is Palindrome	Easy
11	Flattening a Linked List	Flattening a Linked List	Medium
12	Given a linked list of 0s, 1s and 2s, sort it	Given a linked list of 0s, 1s and 2s, sort it	Easy
13	Remove duplicate	Remove duplicate	Easy
14	Find length of Loop	Find length of Loop	Easy
15	Remove duplicates from an unsorted linked list	Remove duplicates from an unsorted linked list	Easy
16	Reverse a Doubly Linked List	Reverse a Doubly Linked List	Easy
17	Segregate even and odd nodes in a Link List	Segregate even and odd nodes in a Link List	Easy
18	Delete nodes having greater value on right	Delete nodes having greater value on right	Medium
20	Add 1 to a number represented as linked list	Add 1 to a number represented as linked list	Easy
21	Merge Sort for Linked List	Merge Sort for Linked List	Easy
22	Quick Sort on Linked List	Quick Sort on Linked List	Medium
23	Middle of the Linked List	Middle of the Linked List	Medium
24	Split a Circular Linked List into two halves	Split a Circular Linked List into two halves	Medium
25	Clone a linked list with next and random pointer	Clone a linked list with next and random pointer	Medium
26	Reverse Nodes in k-Group	Reverse Nodes in k-Group	Medium
27	Reverse Linked List II	Reverse Linked List II	Medium
28	Flatten Binary Tree to Linked List	Flatten Binary Tree to Linked List	Medium
29	Swapping Nodes in a Linked List	Swapping Nodes in a Linked List	Medium
30	Merge In Between Linked Lists	Merge In Between Linked Lists	Medium
31	Delete node in Doubly Linked List	Delete node in Doubly Linked List	Basic

Tree

S.No	Question Link	Solution	Difficulty
1	Left View of Binary Tree	Left View of Binary Tree	Easy
2	Count Leaves in Binary Tree	Count Leaves in Binary Tree	Basic
3	Diameter of Binary Tree	Diameter of Binary Tree	Easy
4	Height of Binary Tree	Height of Binary Tree	Basic
5	Check for Balanced Tree	Check for Balanced Tree	Easy
6	Symmetric Tree	Symmetric Tree	Easy
7	Identical Tree	Identical Tree	Easy
8	Connect Nodes at Same Level	Connect Nodes at Same Level	Medium
9	Level order traversal in spiral form	Level order traversal in spiral form	Easy
10	Level order traversal	Level order traversal	Easy
11	Inorder Traversal	Inorder Traversal	Easy
12	Preorder Traversal	Preorder Traversal	Easy
13	Postorder Traversal	Postorder Traversal	Easy
14	Delete without head pointer	Delete without head pointer	Medium
15	Reverse Level Order Traversal	Reverse Level Order Traversal	Easy
16	Invert Binary Tree	Invert Binary Tree	Easy
17	Right View of Binary Tree	Right View of Binary Tree	Easy
18	Top View of Binary Tree	Top View of Binary Tree	Medium
19	Bottom View of Binary Tree	Bottom View of Binary Tree	Medium
20	Minimum Depth of Binary Tree	Minimum Depth of Binary Tree	Easy
21	ZigZag Tree Traversal	ZigZag Tree Traversal	Easy
22	Diagonal Traversal of Binary Tree	Diagonal Traversal of Binary Tree	Medium
23	Check if Tree is Isomorphic	Check if Tree is Isomorphic	Medium
24	Lowest Common Ancestor in a Binary Tree	Lowest Common Ancestor in a Binary Tree	Medium
25	Binary Tree to DLL	Binary Tree to DLL	Hard
26	Boundary Traversal of binary tree	Boundary Traversal of binary tree	Medium
27	Construct Tree from Inorder & Preorder	Construct Tree from Inorder & Preorder	Medium
28	Sum Tree	Sum Tree	Medium
29	Duplicate subtree in Binary Tree	Duplicate subtree in Binary Tree	Medium
30	Duplicate Subtrees	Duplicate Subtrees	Medium
31	Maximum sum of Non-adjacent nodes	Maximum sum of Non-adjacent nodes	Medium
32	Sum of nodes on the longest path from root to leaf node	Sum of nodes on the longest path from root to leaf node	Easy
33	Clone a Binary Tree	Clone a Binary Tree	Medium
34	K distance from root	K distance from root	Easy
35	Diagonal Sum In Binary Tree	Diagonal Sum In Binary Tree	Easy
36	Perfect Binary Tree	Perfect Binary Tree	Easy
37	Leaves to DLL	Leaves to DLL	Medium

Binary Search Tree

S.No	Question Link	Solution	Difficulty
1	Check for BST	Check for BST	Medium
2	Lowest Common Ancestor in a BST	Lowest Common Ancestor in a BST	Medium
3	Largest BST	Largest BST	Medium
4	Insert a node in a BST	Insert a node in a BST	Basic
5	Minimum element in BST	Minimum element in BST	Basic
6	Count BST nodes that lie in a given range	Count BST nodes that lie in a given range	Medium
7	Flatten BST To A Sorted List	Flatten BST To A Sorted List	Medium
8	Preorder to Postorder	Preorder to Postorder	Medium
9	Normal BST to Balanced BST	Normal BST to Balanced BST	Easy

Stack and Queue

S.No	Question Link	Solution	Difficulty
1	Reverse Stack Using Recursion	Reverse Stack Using Recursion	Easy
2	Sort a stack	Sort a stack	Easy
3	Merge Intervals	Merge Intervals	Medium
4	Valid Substring	Valid Substring	Easy
5	LRU Cache	LRU Cache	Easy
6	Queue Reversal	Queue Reversal	Easy
7	Implement two stacks in an array	Implement two stacks in an array	Easy
8	Next Smaller Element	Next Smaller Element	Medium
9	First non-repeating character in a stream	First non-repeating character in a stream	Medium
10	Game with String	Game with String	Medium
11	First negative integer in every window of size k	First negative integer in every window of size k	Medium
12	Reverse First K elements of Queue	Reverse First K elements of Queue	Easy
13	Maximum of all subarrays of size k	Maximum of all subarrays of size k	Medium
14	Rotten Oranges	Rotten Oranges	Medium
15	Special Stack	Special Stack	Medium
16	Queue using two Stacks	Queue using two Stacks	Easy
17	Flood fill Algorithm	Flood fill Algorithm	Medium
18	Distance of nearest cell having 1	Distance of nearest cell having 1	Medium
19	Circular tour	Circular tour	Medium

Dynamic Programming

S.No	Question Link	Solution	Difficulty
1	Min Cost Climbing Stairs	Min Cost Climbing Stairs	Easy
2	Coin Change	Coin Change	Medium
3	0 - 1 Knapsack Problem	0 - 1 Knapsack Problem	Medium
4	nCr	nCr	Medium
5	House Robber	House Robber	Medium
6	House Robber II	House Robber II	Medium
7	Jump Game	Jump Game	Medium
8	Longest Increasing Subsequence	Longest Increasing Subsequence	Medium
9	Longest Common Subsequence	Longest Common Subsequence	Medium
10	Maximum path sum in matrix	Maximum path sum in matrix	Medium
11	Edit Distance	Edit Distance	Medium
12	House Robber III	House Robber III	Medium
13	Minimum sum partition	Minimum sum partition	Hard
14	Subset Sum Problem	Subset Sum Problem	Medium
15	Partition Equal Subset Sum	Partition Equal Subset Sum	Medium
16	Knapsack with Duplicate Items	Knapsack with Duplicate Items	Medium
17	Rod Cutting	Rod Cutting	Medium
18	Coin Change 2	Coin Change 2	Medium
19	Longest Common Substring	Longest Common Substring	Medium
20	Longest Palindromic Subsequence	Longest Palindromic Subsequence	Medium
21	Minimum number of deletions and insertions	Minimum number of deletions and insertions	Easy
22	Shortest Common Supersequence	Shortest Common Supersequence	Medium
23	Minimum number of deletions	Minimum number of deletions	Easy
24	Longest Repeating Subsequence	Longest Repeating Subsequence	Easy

Mathematics

S.No	Question Link	Solution	Difficulty
1	Find Nth root of M	Find Nth root of M	Easy
2	Kth Smallest Factor	Kth Smallest Factor	Easy
3	Square root of a number	Square root of a number	Medium

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Must Do Coding Questions in Java