Top 100 DSA Interview Questions
2026 Guide with detailed explanations, complexity analysis, and visual diagrams to master Data Structures & Algorithms for technical interviews.
100 Questions
8 Key Topics
Complexity Analysis
Updated for 2026
Top Interview Questions
1. Two Sum
Easy
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
2. Reverse a Linked List
Easy
Reverse a singly linked list in-place and return the new head.
3. Valid Parentheses
Easy
Given a string s containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid.
4. Merge Intervals
Medium
Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals.
5. Binary Tree Level Order Traversal
Medium
Given the root of a binary tree, return the level order traversal of its nodes’ values.
6. Clone Graph
Medium
Given a reference of a node in a connected undirected graph, return a deep copy (clone) of the graph.
7. Longest Palindromic Substring
Medium
Given a string s, return the longest palindromic substring in s.
8. Trapping Rain Water
Hard
Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
Key DSA Visualizations
Time Complexity Comparison
O(1)
O(log n)
O(n)
O(n²)
Binary Search Tree
Node
Root
