Top 100 Coding Interview Questions: The Ultimate Cheat Sheet (DSA)

Top 100 Coding Interview Questions: The Ultimate Cheat Sheet (DSA)

You don't need to solve 1000 LeetCode problems. You need to solve the right 100 problems. Patterns repeat. If you master these 100, you can solve almost any variation asked in interviews at Amazon, Google, Microsoft, or startups.

Here is the curated list, categorized by topic.

1. Arrays (The Basics)

1. Two Sum (The most famous question).
2. Best Time to Buy and Sell Stock (Valley-Peak approach).
3. Contains Duplicate.
4. Product of Array Except Self (No division allowed).
5. Maximum Subarray (Kadane’s Algorithm).
6. Maximum Product Subarray.
7. Find Minimum in Rotated Sorted Array.
8. Search in Rotated Sorted Array.
9. 3Sum.
10. Container With Most Water.

2. Strings

1. Valid Anagram.
2. Valid Palindrome.
3. Longest Substring Without Repeating Characters (Sliding Window).
4. Longest Palindromic Substring.
5. Group Anagrams.
6. Valid Parentheses (Stack).

3. Linked Lists

1. Reverse a Linked List (Iterative & Recursive).
2. Detect Cycle in a Linked List (Floyd’s Cycle Finding).
3. Merge Two Sorted Lists.
4. Remove Nth Node From End of List.
5. Reorder List.
6. Merge K Sorted Lists (Hard).

4. Trees & Graphs

1. Maximum Depth of Binary Tree.
2. Same Tree.
3. Invert Binary Tree (Google Classic).
4. Binary Tree Level Order Traversal (BFS).
5. Subtree of Another Tree.
6. Lowest Common Ancestor (LCA).
7. Validate Binary Search Tree.
8. Number of Islands (Graph BFS/DFS).
9. Clone Graph.
10. Course Schedule (Topological Sort).

5. Dynamic Programming (DP)

1. Climbing Stairs (Fibonacci).
2. Coin Change.
3. Longest Increasing Subsequence (LIS).
4. Longest Common Subsequence (LCS).
5. Word Break.
6. House Robber.
7. Unique Paths (Grid).
8. Jump Game.

6. Sorting & Searching

1. Merge Sort Implementation.
2. Quick Sort Implementation.
3. Binary Search.
4. Top K Frequent Elements (Heap).
5. Kth Largest Element in an Array.

How to Practice?

Step 1: Brute Force

Don't jump to the optimal solution. First, say the O(N^2) solution aloud. It shows you can think.

Step 2: Optimize

"Can we do this in O(N)? Can we use a Hash Map?"

Step 3: Dry Run

Write code on paper (or Google Doc). In interviews, you won't always have a compiler to tell you syntax errors.

Behavioral Tips for Coding Interviews

1. Think Aloud: Never stay silent for 5 minutes. The interviewer wants to hear your thought process.
2. Clarify Constraints: "Is the array sorted?", "Can numbers be negative?", "What if the input is empty?" Asking these questions before coding earns huge points.
3. Test Cases: After writing code, manually run a test case through it to catch bugs yourself.

Resources

• LeetCode: The Gold standard.
• NeetCode.io: Excellent video explanations for these 150 questions.
• GeeksForGeeks: Great for reading theory.

Code, Compile, Conquer. Practice these questions in our specialized coding playground on Sproutern