chiphuyen / Coding Exercises

This repository contains my implementation of useful data structures, algorithms, games, as well as my solutions to programming puzzles.

Each item is marked with a difficulty level. 1 - easy 2 - medium 3 - hard

If a file name starts with 'lc', it's a problem from leetcode.com

Written in python3. Thanks Danijar Hafner (@danijar) for the inspiration.

Data structures

Linked lists

• [x] List class (linked_list.py) - 1
• [ ] Remove duplicates (linked_list_algos.py)
• [ ] Find nth last element (linked_list_algos.py)
• [ ] Remove node given only its object (linked_list_algos.py)
• [ ] Sum linked lists with one digit per node (linked_list_algos.py)
• [ ] Find beginning of circle (linked_list_algos.py)

Trees

• [x] Binary heap class (binary_heap.py) - 2

• [ ] Binary tree class (binary_tree.py) - 1

• [x] Binary search tree class that allows duplicate values (binary_search_tree.py) - 2

  BST class inherits binary tree class
  

• [ ] Red black tree class (red_black_tree.py)

• [ ] B+ tree class (b_tree.py) - 3

• [x] Trie class that allows word removal (trie.py) - 2

• [x] Check if a binary tree is a binary search tree (binary_tree_algos.py) - 2

• [ ] Check if a binary tree is balanced (binary_tree_algos.py)

• [ ] Find first common ancestor of two nodes in a binary tree (binary_tree_algos.py)

• [ ] Get all nodes of depth n in a binary tree (binary_tree_algos.py)

• [ ] Given two large trees, check if the first is a subtree of the second (binary_tree_algos.py)

• [ ] Find all sub paths in a binary tree that sum up to x (binary_tree_algos.py)

• [ ] Create a balanced binary search tree from a sorted array (bst_algos.py)

Graphs

• [ ] Undirected graph class
• [ ] Directed graph class
• [ ] Breadth first search (search.py)
• [ ] Depth first search (search.py)
• [ ] A-star (search.py)

Stacks and queues

• [ ] Queue class (queue.py)
• [x] Heap priority queue (priority_queue.py) - 1
• [ ] Stack class (stack.py)
• [ ] Stack that finds min in O(1) (min_stack.py)
• [ ] Solve Hanoi towers using stacks (stack_algos.py)
• [ ] Sort stack using only push, pop, peek and empty (stack_algos.py)
• [ ] Build a queue using two stacks (stack_algos.py)

Algorithms

Sorting

• [x] Insertion sort (sort.py) - 1
• [x] Selection sort (sort.py) - 1
• [x] Merge sort (sort.py) - 2
• [x] Heap sort (sort.py) - 2
• [x] Quick sort (sort.py) - 2
• [x] Counting sort (sort.py) - 2
• [x] Radix sort (sort.py) - 2
• [x] Bucket sort (sort.py) - 2

Dynamic Programming

• [ ] Computing a Fibonacci sequence
• [ ] Find the longest common subsequence between two strings

Recursion

• [ ] Find all permutations of a string
• [ ] Find all subsets of a set
• [ ] Find all proper combinations of n parentheses
• [ ] Bucket fill
• [ ] Check if it's possible to make a change with a set of coins
• [ ] Check if it's possible to weight two objects with a set of weights
• [ ] Eight queen

Programming Puzzles

String Manipulation

• [x] Check if two strings are anagrams in O(n + m) time (anagrams.py) - 1
• [x] Find the longest palindromic substring in O(n^2) time (lc_longest_palindrome.py) - 2
• [x] Check if a string has balanced delimiters in O(n) time (delim_balanced.py) - 2
• [x] Reverse words while maintaining spaces and tabs in O(n) time (reverse_words.py) - 2
• [x] Longest substring without repeating characters in O(n) time (lc_longest_nonrepeat_substring.py) - 2
• [x] Longest contiguous substring of 2 distinct characters in O(n) time (substring_two_chars.py) - 2
• [ ] Remove duplicate chars in a string
• [ ] Encode and decode Caesar cipher (caesar.py)
• [ ] Check if a string is a rotation of another

Mathematical

• [x] Reverse integers (lc_reverse_int.py) - 1

• [x] Sieve of Eratosthenes (sieve_prime.py) - 1

• [x] Two sum in O(n) time (lc_two_sum.py) - 1

  Given an array of integers, return indices of the two numbers 
  such that they add up to a specific target.
  

• [x] Year with maximum population (year_max_pop.py) - 1

  Given a list of people with their years of birth and death, 
  find the year with max population
  

• [x] FizzBuzz (fizzbuzz.py) - 1

• [x] ZigZag conversion (lc_zigzag_convert.py) - 2

• [x] Find sum of all subarrays of an array (subarray_sum.py) - 2

• [x] Add two numbers, each represented by a reverse linked list (lc_add_number_reverse.py) - 2

• [x] Find the median of two sorted arrays in O(log(m+n)) time (lc_median_arrays.py) - 3

• [ ] Find nth smallest number that can be created using a list of prime factors

• [ ] Count occurences of given digit in all numbers up to n

• [ ] Rotate N x N matrix in place

Games

• [x] Game of ghost (ghost.py) - 3

  Ghost is a word game in which players take turns adding letters to a
  growing word fragment, trying not to be the one to complete a valid word.
  
  This implementation uses minimax with alpha-beta pruning to make sure the computer always wins.
  It uses a Trie to keep track of the dictionary.