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Top DSA questions asked in product based companies↗️📝

Here's a detailed and categorized list of frequently asked Data Structures and Algorithms (DSA) questions in product-based companies like Google, Amazon, Microsoft, Adobe, Atlassian, Uber, and others.

📌 1. Arrays & Strings

These are the most basic and frequently asked.

Here are the LeetCode links for all the problems you've listed:

1. Two Sum (Leetcode 1)

🔗 https://leetcode.com/problems/two-sum/

2. Best Time to Buy and Sell Stock (Leetcode 121)

🔗 https://leetcode.com/problems/best-time-to-buy-and-sell-stock/

3. Kadane’s Algorithm – Maximum Subarray (Leetcode 53)

🔗 https://leetcode.com/problems/maximum-subarray/

4. Merge Intervals (Leetcode 56)

🔗 https://leetcode.com/problems/merge-intervals/

5. Set Matrix Zeroes (Leetcode 73)

🔗 https://leetcode.com/problems/set-matrix-zeroes/

6. Rotate Image / Matrix 90 Degrees (Leetcode 48)

🔗 https://leetcode.com/problems/rotate-image/

7. Longest Consecutive Sequence (Leetcode 128)

🔗 https://leetcode.com/problems/longest-consecutive-sequence/

8. Trapping Rain Water (Leetcode 42)

🔗 https://leetcode.com/problems/trapping-rain-water/

9. Product of Array Except Self (Leetcode 238)

🔗 https://leetcode.com/problems/product-of-array-except-self/

10. Sliding Window Maximum (Leetcode 239)

🔗 https://leetcode.com/problems/sliding-window-maximum/

📌 2. Hashing / HashMap / HashSet

Here are the LeetCode links for the additional problems you listed:

1. Subarray Sum Equals K (Leetcode 560)

🔗 https://leetcode.com/problems/subarray-sum-equals-k/

2. Group Anagrams (Leetcode 49)

🔗 https://leetcode.com/problems/group-anagrams/

3. Top K Frequent Elements (Leetcode 347)

🔗 https://leetcode.com/problems/top-k-frequent-elements/

4. Longest Substring Without Repeating Characters (Leetcode 3)

🔗 https://leetcode.com/problems/longest-substring-without-repeating-characters/

5. Longest Palindromic Substring (Leetcode 5)

🔗 https://leetcode.com/problems/longest-palindromic-substring/

6. Minimum Window Substring (Leetcode 76)

🔗 https://leetcode.com/problems/minimum-window-substring/

7. Isomorphic Strings (Leetcode 205)

🔗 https://leetcode.com/problems/isomorphic-strings/

📌 3. Two Pointers / Fast & Slow Pointers

Here are the LeetCode links for the problems in your latest list:

1. Container With Most Water (Leetcode 11)

🔗 https://leetcode.com/problems/container-with-most-water/

2. 3Sum (Leetcode 15)

🔗 https://leetcode.com/problems/3sum/

3. 4Sum (Leetcode 18)

🔗 https://leetcode.com/problems/4sum/

4. Remove Duplicates from Sorted Array (Leetcode 26)

🔗 https://leetcode.com/problems/remove-duplicates-from-sorted-array/

5. Move Zeroes (Leetcode 283)

🔗 https://leetcode.com/problems/move-zeroes/

6. Linked List Cycle (Leetcode 141)

🔗 https://leetcode.com/problems/linked-list-cycle/

7. Intersection of Two Linked Lists (Leetcode 160)

🔗 https://leetcode.com/problems/intersection-of-two-linked-lists/

8. Palindrome Linked List (Leetcode 234)

🔗 https://leetcode.com/problems/palindrome-linked-list/

📌 4. Sorting & Searching

Here are the LeetCode links (and related links for sorting problems) for the new list of problems:

1. ✅ Merge Sort / Quick Sort (Implementations)

While not directly asked in LeetCode, you can implement them as practice. Here are related problems:

2. 🔍 Binary Search on Sorted Array (Leetcode 704)

🔗 https://leetcode.com/problems/binary-search/

3. 🔄 Search in Rotated Sorted Array (Leetcode 33)

🔗 https://leetcode.com/problems/search-in-rotated-sorted-array/

4. ⚖️ Median of Two Sorted Arrays (Leetcode 4)

🔗 https://leetcode.com/problems/median-of-two-sorted-arrays/

5. 🔢 Kth Largest Element in an Array (Leetcode 215)

🔗 https://leetcode.com/problems/kth-largest-element-in-an-array/

6. 🔁 Count Inversions in Array

Not available on LeetCode directly, but very common on:

7. 🧭 Search a 2D Matrix (Leetcode 74)

🔗 https://leetcode.com/problems/search-a-2d-matrix/

📌 5. Recursion & Backtracking

Here are the LeetCode links for the backtracking and combinatorics problems you listed:

1. ✅ Subsets (Leetcode 78)

🔗 https://leetcode.com/problems/subsets/

2. ✅ Subsets II (Leetcode 90)

🔗 https://leetcode.com/problems/subsets-ii/

3. 🔁 Permutations (Leetcode 46)

🔗 https://leetcode.com/problems/permutations/

4. 🔁 Permutations II (Leetcode 47)

🔗 https://leetcode.com/problems/permutations-ii/

5. 👑 N-Queens (Leetcode 51)

🔗 https://leetcode.com/problems/n-queens/

6. 🧩 Sudoku Solver (Leetcode 37)

🔗 https://leetcode.com/problems/sudoku-solver/

7. 🔍 Word Search (Leetcode 79)

🔗 https://leetcode.com/problems/word-search/

8. ➕ Combination Sum (Leetcode 39)

🔗 https://leetcode.com/problems/combination-sum/

9. ➕ Combination Sum II (Leetcode 40)

🔗 https://leetcode.com/problems/combination-sum-ii/

10. ☎️ Letter Combinations of a Phone Number (Leetcode 17)

🔗 https://leetcode.com/problems/letter-combinations-of-a-phone-number/

📌 6. Linked Lists

Here are solid links from LeetCode (or similar trusted sites) for each of your linked list topics:

  1. Reverse Linked List
    https://leetcode.com/problems/reverse-linked-list/

  2. Detect Cycle in Linked List
    https://leetcode.com/problems/linked-list-cycle/

  3. Merge Two Sorted Lists
    https://leetcode.com/problems/merge-two-sorted-lists/

  4. Add Two Numbers (Linked List based)
    https://leetcode.com/problems/add-two-numbers/

  5. LRU Cache (Design)
    https://leetcode.com/problems/lru-cache/

  6. Copy List with Random Pointer
    https://leetcode.com/problems/copy-list-with-random-pointer/

  7. Flatten a Multilevel Doubly Linked List
    https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list/

  8. Merge K Sorted Lists
    https://leetcode.com/problems/merge-k-sorted-lists/

📌 7. Trees & Binary Trees

Here are the LeetCode links for your list of binary tree problems, covering traversal, construction, depth, and more:

1. 🌳 Maximum Depth of Binary Tree (Leetcode 104)

🔗 https://leetcode.com/problems/maximum-depth-of-binary-tree/

2. 📏 Diameter of Binary Tree (Leetcode 543)

🔗 https://leetcode.com/problems/diameter-of-binary-tree/

3. 🔁 Inorder / Preorder / Postorder Traversal

You can solve each using **recursive* and iterative approaches.*

4. 📶 Level Order Traversal / Zigzag Level Order

5. 🔁 Symmetric Tree (Leetcode 101)

🔗 https://leetcode.com/problems/symmetric-tree/

6. 🧬 Lowest Common Ancestor of a Binary Tree (Leetcode 236)

🔗 https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/

7. 🔐 Serialize and Deserialize Binary Tree (Leetcode 297)

🔗 https://leetcode.com/problems/serialize-and-deserialize-binary-tree/

8. 🏗️ Construct Binary Tree from Inorder and Preorder/Postorder Traversal

📌 8. Binary Search Trees (BST)

Here are the LeetCode links for your list of Binary Search Tree (BST) problems:

1. ✅ Validate Binary Search Tree (Leetcode 98)

🔗 https://leetcode.com/problems/validate-binary-search-tree/

2. 🔢 Kth Smallest Element in a BST (Leetcode 230)

🔗 https://leetcode.com/problems/kth-smallest-element-in-a-bst/

3. 🌲 Convert Sorted Array to BST (Leetcode 108)

🔗 https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

4. ❌ Delete Node in a BST (Leetcode 450)

🔗 https://leetcode.com/problems/delete-node-in-a-bst/

5. 🧬 Lowest Common Ancestor of a BST (Leetcode 235)

🔗 https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/

6. 🧭 BST Iterator (Leetcode 173)

🔗 https://leetcode.com/problems/binary-search-tree-iterator/

📌 9. Heaps / Priority Queue

Here are the LeetCode links for your list of heap/priority queue-based and advanced data structure problems:

1. 🔢 Kth Largest Element in an Array (Leetcode 215)

🔗 https://leetcode.com/problems/kth-largest-element-in-an-array/

2. 🆙 Top K Frequent Words (Leetcode 692)

🔗 https://leetcode.com/problems/top-k-frequent-words/

3. 🔀 Merge K Sorted Lists (Leetcode 23)

🔗 https://leetcode.com/problems/merge-k-sorted-lists/

4. 🔁 Reorganize String (Leetcode 767)

🔗 https://leetcode.com/problems/reorganize-string/

5. 📊 Find Median from Data Stream (Leetcode 295)

🔗 https://leetcode.com/problems/find-median-from-data-stream/

6. 📉 Sliding Window Maximum (Leetcode 239)

🔗 https://leetcode.com/problems/sliding-window-maximum/

📌 10. Stack & Monotonic Stack

Here are the LeetCode links for your list of stack-based problems (classic interview questions):

1. ✅ Valid Parentheses (Leetcode 20)

🔗 https://leetcode.com/problems/valid-parentheses/

2. 📦 Min Stack (Leetcode 155)

🔗 https://leetcode.com/problems/min-stack/

Design problem using stack with constant-time min retrieval.

3. 🟫 Largest Rectangle in Histogram (Leetcode 84)

🔗 https://leetcode.com/problems/largest-rectangle-in-histogram/

Classic monotonic stack problem.

4. 🌡️ Daily Temperatures (Leetcode 739)

🔗 https://leetcode.com/problems/daily-temperatures/

Monotonic decreasing stack used to find next warmer day.

5. 🔁 Next Greater Element I (Leetcode 496)

🔗 https://leetcode.com/problems/next-greater-element-i/

6. 🔁 Next Greater Element II (Leetcode 503)

🔗 https://leetcode.com/problems/next-greater-element-ii/

7. ☄️ Asteroid Collision (Leetcode 735)

🔗 https://leetcode.com/problems/asteroid-collision/

📌 11. Queues & Deque

Here are the LeetCode links for your list of queues, stacks, and BFS/graph traversal problems:

1. 🔁 Implement Queue using Stacks (Leetcode 232)

🔗 https://leetcode.com/problems/implement-queue-using-stacks/

Use two stacks to simulate FIFO behavior.

2. 📦 LRU Cache (Leetcode 146)

🔗 https://leetcode.com/problems/lru-cache/

Design question using HashMap + Doubly Linked List.

3. 📉 Sliding Window Maximum (Leetcode 239)

🔗 https://leetcode.com/problems/sliding-window-maximum/

Can be solved using Deque or Heap.

4. 🍊 Rotting Oranges (Leetcode 994)

🔗 https://leetcode.com/problems/rotting-oranges/

Classic BFS in a grid problem.

5. 🔢 Shortest Path in Binary Matrix (Leetcode 1091)

🔗 https://leetcode.com/problems/shortest-path-in-binary-matrix/

Another BFS grid traversal problem with 8 directions.

📌 12. Graphs (BFS / DFS / Union-Find)

Here are the LeetCode links for your list of graph and related problems (covering DFS, BFS, Union-Find, Topological Sort, and shortest path algorithms):

1. 🏝️ Number of Islands (Leetcode 200)

🔗 https://leetcode.com/problems/number-of-islands/

Classic DFS/BFS grid problem.

2. 🕸️ Clone Graph (Leetcode 133)

🔗 https://leetcode.com/problems/clone-graph/

DFS/BFS + HashMap for graph cloning.

3. 📚 Course Schedule (Leetcode 207)

🔗 https://leetcode.com/problems/course-schedule/

Topological Sort / Cycle detection in directed graph.

4. 🔄 Word Ladder (Leetcode 127)

🔗 https://leetcode.com/problems/word-ladder/

BFS shortest path in word graph.

5. 🌊 Pacific Atlantic Water Flow (Leetcode 417)

🔗 https://leetcode.com/problems/pacific-atlantic-water-flow/

Multi-source BFS/DFS on matrix.

6. 🔄 Detect Cycle in Directed/Undirected Graph

  • Directed Graph cycle detection (Leetcode 207 / 210 variants)
  • Undirected Graph cycle detection (Leetcode 261 / custom)

Use DFS or Union-Find.

7. 🔗 Union-Find Problems (Connected Components)

8. 📡 Network Delay Time (Leetcode 743)

🔗 https://leetcode.com/problems/network-delay-time/

Use Dijkstra’s algorithm.

9. 🛣️ Dijkstra’s Algorithm / Bellman-Ford Algorithm

Here you go — solid links for your graph shortest path topics:

  1. Dijkstra’s Algorithm (LeetCode 743 - Network Delay Time)
    https://leetcode.com/problems/network-delay-time/

  2. Bellman-Ford Algorithm Tutorials (no direct LeetCode problem)

📌 13. Greedy Algorithms

1. 🏃‍♂️ Jump Game I (Leetcode 55)

🔗 https://leetcode.com/problems/jump-game/

2. 🏃‍♂️ Jump Game II (Leetcode 45)

🔗 https://leetcode.com/problems/jump-game-ii/

3. ⛽ Gas Station (Leetcode 134)

🔗 https://leetcode.com/problems/gas-station/

4. 🎯 Partition Labels (Leetcode 763)

🔗 https://leetcode.com/problems/partition-labels/

5. 🎈 Minimum Number of Arrows to Burst Balloons (Leetcode 452)

🔗 https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/

6. 📅 Activity Selection Problem

7. 🔀 Merge Intervals (Leetcode 56)

🔗 https://leetcode.com/problems/merge-intervals/

8. 📆 Interval Scheduling

  • Interval scheduling maximization is essentially the same as the activity selection problem;
  • For interval scheduling variants, see Non-overlapping Intervals (Leetcode 435) above.

📌 14. Dynamic Programming (DP)

Very important for top product companies.

🧱 1D DP

Here are the LeetCode links for your list of classic dynamic programming (DP) problems:

1. 🔢 Fibonacci Number (Leetcode 509)

🔗 https://leetcode.com/problems/fibonacci-number/

2. 🧗‍♂️ Climbing Stairs (Leetcode 70)

🔗 https://leetcode.com/problems/climbing-stairs/

3. 🏠 House Robber I (Leetcode 198)

🔗 https://leetcode.com/problems/house-robber/

4. 🏠 House Robber II (Leetcode 213)

🔗 https://leetcode.com/problems/house-robber-ii/

5. ➕ Maximum Subarray (Kadane’s Algorithm) (Leetcode 53)

🔗 https://leetcode.com/problems/maximum-subarray/

6. 💰 Coin Change (Leetcode 322)

🔗 https://leetcode.com/problems/coin-change/

7. 📈 Longest Increasing Subsequence (Leetcode 300)

🔗 https://leetcode.com/problems/longest-increasing-subsequence/

🧱 2D DP

Here are the LeetCode links for your advanced dynamic programming problems:

1. 📏 Longest Common Subsequence (LCS)

2. ✏️ Edit Distance (Levenshtein Distance)

3. 🔗 Matrix Chain Multiplication

4. 🎒 0/1 Knapsack

5. 🚗 Unique Paths

6. ➖ Minimum Path Sum

7. 🔄 Palindromic Substrings

8. 🌟 Wildcard Matching (Leetcode 44)

🔗 https://leetcode.com/problems/wildcard-matching/
Regex Matching (Leetcode 10)
🔗 https://leetcode.com/problems/regular-expression-matching/

🧱 DP on Trees / Graphs

Here are the LeetCode links and explanations for your requested problems involving trees, DP on DAG, and word break:

1. 🌲 Maximum Path Sum in Binary Tree (Leetcode 124)

🔗 https://leetcode.com/problems/binary-tree-maximum-path-sum/

Find the max sum path which can start and end anywhere in the binary tree.

2. 🔀 DP on DAG (Longest Path)

  • Leetcode doesn’t have a direct “Longest Path in DAG” problem, but closely related:

3. 🧩 Word Break (Leetcode 139)

🔗 https://leetcode.com/problems/word-break/

Use DP to check if string can be segmented into dictionary words.

📌 15. Tries (Prefix Trees)

Here are the LeetCode links for your Trie and advanced string problems:

1. 🌲 Implement Trie (Prefix Tree)

🔗 208. Implement Trie (Prefix Tree)

Insert, search, and prefix matching in a Trie data structure.

2. 🔎 Word Search II

🔗 212. Word Search II

Use Trie + DFS for multiple word searching on a board.

3. 🔄 Replace Words

🔗 648. Replace Words

Use Trie to replace words with their roots.

4. 🔗 Palindrome Pairs

🔗 336. Palindrome Pairs

Use Trie and hashing techniques to find pairs of words that form palindromes.

📌 16. Bit Manipulation

Here are the LeetCode links for your bit manipulation problems:

1. ☝️ Single Number (Leetcode 136)

🔗 https://leetcode.com/problems/single-number/

Find the element that appears once when every other element appears twice.

2. ☝️☝️ Single Number II (Leetcode 137)

🔗 https://leetcode.com/problems/single-number-ii/

Find the element that appears once when every other element appears thrice.

3. 🔢 Number of 1 Bits (Leetcode 191)

🔗 https://leetcode.com/problems/number-of-1-bits/

Count the number of set bits (1s) in an integer.

4. 🧮 Counting Bits (Leetcode 338)

🔗 https://leetcode.com/problems/counting-bits/

For every number i in [0, n], count the number of 1s in binary representation.

5. ❌ XOR of all elements

  • This is typically part of problems like Single Number.
  • You can XOR all elements to get the unique number.
  • No specific LeetCode problem, but example in 136. Single Number.

6. 🔥 Power of Two (Leetcode 231)

🔗 https://leetcode.com/problems/power-of-two/

Check if a number is a power of two using bit manipulation.

7. 📋 Subsets using Bitmasks

  • No direct LeetCode problem titled “Subsets using bitmasks” but related:

    • 78. Subsets — Can be solved by bitmask enumeration.

📌 17. Sliding Window

Here are the LeetCode links for your sliding window & substring problems:

1. 🔍 Minimum Window Substring

🔗 76. Minimum Window Substring

2. 🧩 Longest Substring with At Most K Distinct Characters

🔗 340. Longest Substring with At Most K Distinct Characters

3. 🔁 Longest Repeating Character Replacement

🔗 424. Longest Repeating Character Replacement

4. 🔄 Permutation in String

🔗 567. Permutation in String

5. ➕ Maximum Sum of Subarray of Size K

📌 18. Matrix Problems

Here are the LeetCode links for your 2D matrix and grid problems:

1. 🔄 Spiral Order

🔗 54. Spiral Matrix

2. 🔄 Rotate Image (90 degrees)

🔗 48. Rotate Image

3. 🔍 Word Search

🔗 79. Word Search

4. 0️⃣ Set Matrix Zeroes

🔗 73. Set Matrix Zeroes

5. 🔎 Search in 2D Matrix

🔗 74. Search a 2D Matrix

6. 🏝️ Number of Islands (Island Problems - DFS/BFS)

🔗 200. Number of Islands

📌 19. Design / OOP Based Questions

1. LRU Cache

2. Design Twitter

3. Design Hit Counter

4. Design File System

5. Design Snake Game

  • Objective: Implement the classic Snake game where the player controls a snake to eat food and grow longer without colliding with itself or the walls.
  • Approach: Utilize game loops, collision detection, and score tracking.
  • Resource: Design Snake Game - GeeksforGeeks(GeeksforGeeks)

6. Design Parking Lot

7. Design Browser History

  • Functionality: Implement a browser history feature that supports visiting URLs, navigating back and forward, and managing the history stack.
  • Implementation: Use stacks to manage the history and current state.
  • Resource: Design Browser History - GeeksforGeeks(GeeksforGeeks)

📌 20. Math & Number Theory

Got it! Here is one solid, working link per topic for you:

Sieve of Eratosthenes

  1. https://www.geeksforgeeks.org/sieve-of-eratosthenes/

  2. GCD/LCM
    https://www.khanacademy.org/computing/computer-science/cryptography/modarithmetic/a/the-euclidean-algorithm

  3. Modular Exponentiation
    https://www.geeksforgeeks.org/modular-exponentiation-power-in-modular-arithmetic/

  4. Count Primes
    https://leetcode.com/problems/count-primes/

  5. Excel Sheet Column Title
    https://leetcode.com/problems/excel-sheet-column-title/

  6. Pow(x, n)
    https://leetcode.com/problems/powx-n/

🧠 Bonus: Top 25 DSA Questions for Final Revision

  1. Two Sum
    🔗 1. Two Sum

  2. Longest Substring Without Repeating Characters
    🔗 3. Longest Substring Without Repeating Characters

  3. Merge Intervals
    🔗 56. Merge Intervals

  4. Maximum Subarray
    🔗 53. Maximum Subarray

  5. Merge K Sorted Lists
    🔗 23. Merge k Sorted Lists

  6. Clone Graph
    🔗 133. Clone Graph

  7. Word Ladder
    🔗 127. Word Ladder

  8. Longest Common Subsequence
    🔗 1143. Longest Common Subsequence

  9. LRU Cache
    🔗 146. LRU Cache

  10. Number of Islands
    🔗 200. Number of Islands

  11. Search in Rotated Sorted Array
    🔗 33. Search in Rotated Sorted Array

  12. Median of Two Sorted Arrays
    🔗 4. Median of Two Sorted Arrays

  13. Subsets
    🔗 78. Subsets

  14. 0/1 Knapsack
    (Not on LeetCode, but classic problem; see Knapsack on GeeksforGeeks)

  15. Edit Distance
    🔗 72. Edit Distance

  16. Detect Cycle in Directed Graph
    🔗 207. Course Schedule (Detect Cycle in Directed Graph)

  17. Course Schedule
    🔗 207. Course Schedule

  18. Trie Insert/Search
    🔗 208. Implement Trie (Prefix Tree)

  19. Maximum Path Sum in Binary Tree
    🔗 124. Binary Tree Maximum Path Sum

  20. Largest Rectangle in Histogram
    🔗 84. Largest Rectangle in Histogram

  21. Sliding Window Maximum
    🔗 239. Sliding Window Maximum

  22. Kth Largest Element
    🔗 215. Kth Largest Element in an Array

  23. Minimum Window Substring
    🔗 76. Minimum Window Substring

  24. Gas Station
    🔗 134. Gas Station

  25. N-Queens
    🔗 51. N-Queens

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