AlgoVault

A curated repository to practice, revise, and master Data Structures and Algorithms (DSA). Whether you're preparing for coding interviews or want to brush up on your problem-solving skills, this repo is structured to support topic-wise learning, 200 essential interview problems, and a 20-day rapid revision plan.

What’s Inside:

• 600+ most asked DSA questions
• Topic-wise segregation: Arrays, Trees, Graphs, DP, and more
• Tagging: Difficulty, Revisit Flags, Notes
• 20-Day DSA Revision Plan
• Ideal for intermediate-level candidates targeting top product companies
• Constantly updated with new patterns and edge cases

🎯 Where to Start?

👩‍💻 You are...	👉 Start Here
🧱 A beginner starting DSA	Topic-wise Problems
⏳ Want to cover all concepts in fewer questions	200 Essential DSA Questions
🕒 Have limited time to revise	20-Day Revision Plan
🕒 Last Minute Interview revision	Blind 75 Problems

Topic Wise Problems

Arrays

• Contains Duplicate
• Product of Array except itself *
• Maximum Subarray Sum
• Maximum Product Subarray
• Find Minimum in rotated array *
• Search in Rotated Sorted Array
• 3 Sum
• Container with most water

Linked List

• Remove Nth node from End
• Reverse in K groups
• Merge K sorted Lists

Binary Search

• Binary Search
• Upper Bound
• Lower Bound
• Insert Position
• First and Last Occurence of target
• Number of Occurences in sorted array
• Search in Rotated Sorted Array
• Search in Rotated Sorted Array II
• Minimum in Rotated Sorted array
• kth rotation
• Peak Element

Binary Trees

Easy

• Height of Binary Tree
• Same Tree
• Invert/Flip Binary tree
• Level Order Traversal
• Zigzag Level Order Traversal

Hard

• Maximum Path Sum
• Lowest Common Ancestor
• All Nodes Distance K in Binary Tree
• Burning Tree

Stacks and Queues

Monotonic Stack/Queue [IMP]

• Next Greater Element I
• Next Greater Element II
• Next Smaller Element
• Number of Next Greater Elements
• Trapping Rain Water
• Largest rectangle in a Histogram

Greedy

• Jump Game I
• Jump Game II
• Jump Game III

Sliding Window / Two Pointer

• Binary Array with sum
• Count Nice Subarray
• Minimum size subarray with sum
• Longest Repeating Character Replacement
• Longest Substring Without Repeating Characters

Hashing / Sorting

• Group Anagrams
• Top K Frequent Elements
• Valid Soduko

Graphs

Easy

• Flood Fill

Medium

• Course Schedule - I
• Course Schedule - II
• Course Schedule - IV
• Number of Islands (Matrix version)
• Number of Provinces (Graph version)
• Surrounded Regions
• Rotten Oranges
• Eventual Safe States
• Redundant Connections
• Path with Minimum Effort
• Shortest Path in Binary Matrix
• Word Search
• Cheapest flights within k stops
• Network delay time
• Number of Ways to arrive at destination
• Find City with smallest number of neighbors
• Number of Connected Components

Hard

• Word Ladder
• Alien Dictionary
• Minimum Operations to make Network Connected

Dynamic Programming

1D DP

• Climbing Stairs
• Frog Jump
• Frog Jump with k distance
• House Robber I
• House Robber II
• House Robber III

2D/3D DP - DP on Grids

• Ninja Training
• Unique Paths
• Unique Paths II
• Unique Paths III
• Minimum Falling Path Sum
• Minimum Path Sum
• Cherry Pickup I
• Cherry Pickup II

DP on Subsequences

• Subset Sum equal to target
• Partition Equal Subset Sum
• Count Subsets with Sum k
• Coin change I
• Coin Change II
• Unbound Knapsack
• Rod Cutting

DP on Strings

• Longest Common Subsequences
• Print all longest common subsequence
• Edit Distance
• Longest Palindromic Subsequence
• Minimum Insertion Steps to make string palindrome
• Delete Operation for Two Strings
• Restore IP Addresses

DP on Stocks

• Best Time to Buy and Sell Stocks - I
• Best Time to Buy and Sell Stocks - II
• Best Time to Buy and Sell Stocks - III
• Best Time to Buy and Sell Stocks - IV
• Best Time to Buy and Sell Stocks - V
• Best Time to Buy and Sell Stocks - VI

DP on LIS

• Longest Increasing Subsequence
• Print Longest Increasing Subsequence
• Maximum Sum Increasing Subsequence
• Maximum Length of Bitonic Subsequence
• Number of Longest Increasing Subsequence

Partition DP

• Matrix Chain Multiplication
• Minimum Cost of cut the stick
• Burst Balloons

DP on Squares

• Maximum Rectangle Area with all 1s
• Count square submatrices with all ones
• Maximal Squares

Misc

• 0-1 Knapsack
• Egg Dropping

Binary

• Sum of Two Integers
• Number of Set Bits
• Counting Bits
• Missing Number
• Reverse Bits

Strings

• Minimum Add to Make Parentheses Valid

Design

• LRU Cache
• Design Twitter

Trie

• Longest Word in Dictionary

MISC

• Insert Delete GetRandom O(1)

---

Crack the Code: 200 Essential DSA Questions

• Arrays III

  • Search in 2D matrix
  • Majority Element
  • Grid Unique Paths

• Arrays IV

  • 2 Sum
  • 4 Sum
  • Longest Consecutive Sequence
  • Largest subarray with 0 sum
  • Count Subarray with Given XOR
  • Largest Substring Without Repeat

• Linked List

  • Reverse a Linked List
  • Find middle of linked list
  • Merge two sorted List
  • Remove Nth node from end
  • Add two numbers as Linked List
  • Delete node O(1)
  • Find interjection of Y linked list
  • Detect Cycle in Linked List
  • Reverse in K groups
  • Check Palindrome in LL

• Linked List and Arrays

  • 3 Sum
  • Trapping Rain Water

• Greedy

  • Job Sequencing

• Recursion

  • Subset Sum
  • Subset II
  • Combination Sum - I
  • Combination Sum - II
  • Palindrome Partitioning

• Recursion and Backtracking

  • Permutation of String
  • N Queen
  • Sudoku Solver
  • M coloring problem
  • Rat in a maze
  • Word Break

• Binary Search

• • Single Element
  • Search in Rotated Sorted Array
  • Median of Two sorted Arrays
  • Kth elemeny in Two sorted Arrays
  • Allocate books

• Heaps

  • Binary Heap Implementation
  • Kth Largest
  • Maximum Sum Combination
  • Find Median in Data Stream
  • Merge K sorted Arrays
  • Top k frequent elements

• Stacks and Queues

  • Stack using Array
  • Queue using Array
  • Stack using Queues
  • Queue using Stacks
  • Balanced Parentheses
  • Next Greater Element
  • Next Smaller Element
  • LRU cache
  • LFU Cache
  • Maximum Rectangle in a histogram
  • Sliding Window maximum
  • Implement Min Stack
  • Rotten Oranges
  • Stock Span

• Strings

  • Reverse Words in a String
  • Longest Palindromic Substring
  • Roman to Int and vice-versa
  • Longest Common Prefix
  • String to integer
  • Check Anagrams
  • Count and Say
  • Compare Versions

• Binary Trees - III

  • Binary Tree Maximum Path Sum

• Binary Trees Miscelleneous

  • Flatten Binary Tree to LL
  • Find Median from a Data Stream
  • Kth Largest in a Stream
  • Distinct Numbers in a Window
  • Kth Largest in Unsorted Array
  • Flood Fill

• Binary Search Tree

  • Floor in BST
  • Ceil in BST

• Graphs

  • DFS Traversal
  • BFS Traversal
  • Detect Cycle in Undirected Graph BFS, DFS
  • Detect Cycle in Directed Graph BFS, DFS
  • Topological Sort BFS, DFS
  • Number of islands
  • Bipartite Graph BFS, DFS
  • Strongly Connected Components
  • Shortest Path
    • Dijkstra Algorithm
    • Bellman-Ford Algorithm
    • Floyd Warshall Algorithm
  • Minimum Spanning Tree
    • Kruskal's Algorithm
    • Prim's Algorithm

• Dynamic Programming

  • Maximum Product Subarray
  • Longest Increasing Subsequence
  • Longest Common Subsequence
  • 0-1 Knapsack
  • Edit Distance
  • Maximum Sum Increasing Subsequence
  • Matrix Chain multiplications
  • Minimum Path Sum
  • Coin Change
  • Partition Equal Subset Sum
  • Rod Cutting Problem
  • Egg Dropping
  • Job Sequencing

• Trie

  • Implement Trie
  • Implement Trie 2
  • Complete String
  • Count Distinct Substrings
  • Power Set

---

Blind 75

• Day 1: Array

  • 2 Sum
  • Best Time to Buy and Sell Stock
  • Contains Duplicate
  • Product of Array except itself *
  • Maximum Subarray Sum
  • Maximum Product Subarray
  • Find Minimum in rotated array *
  • Search in Rotated Sorted Array
  • 3 Sum
  • Container with most water

• Day 2: Binary

  • Sum of Two Integers
  • Number of Set Bits
  • Counting Bits
  • Missing Number
  • Reverse Bits

• Day 3: Dynamic Programming

  • Climbing Stairs
  • Coin Change
  • Longest Increasing Subsequence
  • Longest Common Subsequence
  • Combination Sum
  • House Robber I
  • House Robber II
  • Unique Paths
  • Jump Game
  • Decode Ways*
  • Word Break*

• Day 4: Graph

  • Graph clone
  • Course Schedule
  • Pacific Atlantic Water flow *
  • Number of Islands
  • Number of Provinces
  • Alien Dictionary
  • Connected Component
  • Longest Consecutive Sequence

• Day 5: Intervals

  • Insert Interval
  • Merge Intervals
  • Non Overlapping Intervals
  • Missing and Repeating
  • Maximum Meetings
  • Meeting rooms I
  • Meeting rooms II
  • Meeting room III

• Day 6: Linked List

  • Reverse a Linked List
  • Detect Cycle for Linked List
  • Merge two sorted List
  • Merge K sorted List
  • Remove nth node from end
  • Reorder Linked List

• Day 7: Matrix

  • Set Matrix Zeros
  • Spiral Matrix
  • Rotate Image
  • Word Search

• Day 8: Strings

  • Longest Substring Without Repeating Characters
  • Longest Repeating Character Replacement*
  • Minimum Window Substring
  • Valid Anagrams
  • Group Anagrams
  • Check for Balanced Paranthesis
  • Check Palindrome
  • Longest Palindromic Substring*
  • Palindromic Substring*
  • Encode and Decode

• Day 9: Tree

  • Height of a Binary Tree
  • Check if two trees are identical
  • Invert/Flip Binary Tree
  • Maximum Path sum
  • Level Order traversal
  • Level Order traversal in Spiral Order
  • Serialize Deserialize a Tree
  • Subtree of Another Tree
  • Construct Binary tree from postorder ans inorder
  • Check if tree is a BST or BT
  • Find kth Smallest element in BST
  • Find LCA of two nodes in BST
  • Implement Trie
  • Implement Trie II

• Day 10: Heap

  • K most frequent elements
  • Find Median from Data Stream

Rule of Thumb

• Simple problems (LL, arrays) → Know iterative first, recursive optional.
• Tree/Graph DFS, backtracking → Recursive first, iterative optional.
• Dynamic programming → Usually iterative (tabulation) preferred, recursive (memoization) to explain intuition.

Contributions

Pull requests are welcome! Feel free to raise issues or add more problems/solutions with clarity and proper structure.

License

This project is licensed under the MIT License.