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My implementation of useful data structures, algorithms, as well as my solutions to programming puzzles.

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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

  • 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

  • Binary heap class (binary_heap.py) - 2

  • Binary tree class (binary_tree.py) - 1

  • 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

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

  • 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)
  • 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

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

  • Check if two strings are anagrams in O(n + m) time (anagrams.py) - 1
  • Find the longest palindromic substring in O(n^2) time (lc_longest_palindrome.py) - 2
  • Check if a string has balanced delimiters in O(n) time (delim_balanced.py) - 2
  • Reverse words while maintaining spaces and tabs in O(n) time (reverse_words.py) - 2
  • Longest substring without repeating characters in O(n) time (lc_longest_nonrepeat_substring.py) - 2
  • 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

  • Reverse integers (lc_reverse_int.py) - 1

  • Sieve of Eratosthenes (sieve_prime.py) - 1

  • 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.
    
  • 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
    
  • FizzBuzz (fizzbuzz.py) - 1

  • ZigZag conversion (lc_zigzag_convert.py) - 2

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

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

  • 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

  • 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.
    

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My implementation of useful data structures, algorithms, as well as my solutions to programming puzzles.

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