Whether you’re preparing for FAANG interviews or enhancing your DSA skills, this curated list of most important and frequently asked coding questions covers all essential topics.
1. Arrays & Strings
These are the foundation of most technical interviews. Mastering them is crucial.
Two Sum: Find indices of two numbers that add up to a target.
Longest Substring Without Repeating Characters: Use sliding window to find the max unique substring.
Longest Palindromic Substring: Expand from center or use dynamic programming.
Next Permutation: Find the next lexicographically greater permutation.
Majority Element: Use Boyer-Moore Voting Algorithm.
Trapping Rain Water: Two-pointer or stack-based water trapping approach.
Kth Largest Element in an Array: Use max-heap or Quickselect.
Maximum Subarray: Kadane’s Algorithm to find the max sum subarray.
2. Linked Lists
These test your pointer manipulation and memory understanding.
Merge Two Sorted Lists: Iterative or recursive merging of linked lists.
Linked List Cycle: Detect loop using Floyd’s Cycle Detection Algorithm.
Reverse Nodes in K-Group: Reverse every k nodes using a stack or recursion.
3. Trees & Graphs
Common in interviews to evaluate recursive thinking and traversal logic.
Lowest Common Ancestor of a Binary Tree: DFS-based recursive solution.
Number of Islands: Count connected components using DFS or BFS.
4. Heaps / Hashing / Stacks
Important for frequency analysis, ordering, and memory structure problems.
Top K Frequent Elements: Use HashMap + Min-Heap.
Merge Intervals: Sort and merge overlapping intervals.
Rotate Image (90°): Transpose and reverse rows.
5. Searching & Sorting
Critical for building optimized and scalable solutions.
Search in Rotated Sorted Array: Modified binary search approach.
Find the Duplicate Number: Use Floyd’s Tortoise and Hare Algorithm.
6. Dynamic Programming
These problems optimize recursive solutions using memoization or tabulation.
Word Break: DP-based word segmentation check.
7. Design Problems
Tests your real-world system design skills using data structures.
LRU Cache: Implement with HashMap + Doubly Linked List for O(1) operations.
These problems cover most of what you need for interviews. Practice consistently, understand the patterns, and you’ll be interview-ready.
Disclaimer: All problem links direct to LeetCode.com, a platform widely used for coding practice. The content and questions belong to their respective creators and are publicly accessible.