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Algorithms and Data Structures

This is the collection of Algorithms, Data Structures and Interview Questions with solutions. This repository contains my solutions for common algorithmic problems and implementation of Data Structures in Java. I've created this repository to learn about algorithms. I am adding solutions continuously.

Algorithms, Data Structures and more than 300 Problems and Solutions are provided so far.


Here are questions divided by difficulty level:

  1. Easy Questions and Answers
  2. Medium Questions and Answers
  3. Hard Questions and Answers



  1. Rotate Array
  2. Contains Duplicate
  3. Find Peak Element
  4. Maximum Subarray
  5. Kth Largest Element in an Array
  6. Find All Duplicates in an Array
  7. Longest Increasing Subsequence
  8. Rotate Image, matrix
  9. Shuffle an Array
  10. Find Min in Rotated Array
  11. Search in Rotated Array

Linked List

  1. Singly Linked List Implementation
  2. Doubly Linked List Implementation
  3. Delete Node in a Linked List
  4. Palindrome Linked List
  5. Reverse Linked List
  6. Intersection of Two Linked Lists
  7. Linked List Cycle
  8. Remove Nth Node From End of List
  9. Merge Sort List
  10. Find Linked List Cycle
  11. Merge k Sorted Lists
    And many other Linked list problems

Binary Tree

  1. Binary Tree Level Order Traversal
  2. Sum of Left Leaves
  3. Invert Binary Tree
  4. Binary Search Tree Iterator
  5. Binary Tree Postorder Traversal
  6. Binary Tree Preorder Traversal
  7. Flatten Binary Tree to Linked List
  8. Symmetric Tree
  9. Binary Tree Inorder Traversal
  10. Same Tree
  11. Maximum Depth of Binary Tree
  12. Balanced Binary Tree
  13. Minimum Depth of Binary Tree
  14. Sorted List to Balanced Binary Search Tree
  15. Validate Binary Search Tree
  16. Sorted List to Balanced BST
  17. Kth Smallest Element in a BST
  18. Binary Tree Zigzag Level Order Traversal
  19. Delete Node in a BST
  20. Lowest Common Ancestor of BST
  21. Binary Tree Left Side View
  22. Binary Tree Right Side View
  23. Mode in BST
  24. Most Frequent Subtree Sum
  25. Find Largest Element in Each Row
  26. Serialize and Deserialize BT
    And many other tree problems


  1. Integer Break
  2. Reverse Bits
  3. Palindrome Number
  4. Math.pow
  5. Jug and Water Problem
  6. Sieve of Eratosthenes
  7. Fermat's primality
  8. Evaluate Reverse Polish Notation

Stack & Queue

  1. Min Stack
  2. Min Queue
  3. Implement Stack Using Queue
  4. Implement Queue Using Stack
  5. Sort Stack

Dynamic Programming

  1. Fibonacci Numbers
  2. Word Break
  3. Subset Sum
  4. 0/1 Knapsack Problem
  5. Shortest Palindrome (KMP)
  6. Minimum Square Sum
  7. Maximum weight transformation of a String
  8. Coin Change


  1. Union Find
  2. Permutations
  3. Subsets


Sorting And Searching

  1. Bubble Sort
  2. Insertion Sort
  3. Selection Sort
  4. Counting Sort
  5. Binary Search , Lower & Upper Bounds
  6. MergeSort
  7. QuickSort


  1. Breadth First Search (BFS)
  2. Depth First Search (DFS)
  3. Prim's Minimum Spanning Tree (MST)
  4. KrusKal's Minimum Spanning Tree (MST)
  5. Topological Sorting
  6. Shortest Path Dijsktra
  7. Shortest Path Bellman-Ford
  8. A* Heuristic Path Finding
  9. Is Graph Bipartite
  10. Is Graph Connected
  11. Cycle Detection
  12. Undirected Graph Bridge Detection


  1. Rabin Karp Subsequence search
  2. Ransom Note
  3. Reverse String
  4. Longest Common Prefix
  5. Is Anagram
  6. Needle and Haystack
  7. Word Break
  8. Meta Strings

Data Structure:


  1. Binary Search Tree (recursive)
  2. Binary Search Tree (iterative)
  3. AVL Tree
  4. Trie (Prefix tree)
  5. Hashed Array Tree
  6. LRU Cache


Did you find a bug? Any way to do it better? Please feel free to pull-request it. :)