Top 30 Must-Do DSA Problems for SDE Interviews

Here’s a curated list of 30 essential DSA problems that cover arrays, strings, linked lists, trees, stacks, queues, hashing, and searching/sorting. Solving these will prepare you for 60–70% of coding rounds for fresher and early SDE roles.

Arrays

• Two Sum
• Best Time to Buy and Sell Stock
• Contains Duplicate
• Reverse Array (DIY)
• Rotate Array
• Maximum Subarray

Strings

• Valid Palindrome
• Valid Anagram
• Longest Substring Without Repeating Characters
• Reverse Words in a String

Linked List

• Reverse Linked List
• Linked List Cycle
• Merge Two Sorted Lists
• Middle of the Linked List

Trees

• Maximum Depth of Binary Tree
• Binary Tree Level Order Traversal
• Validate Binary Search Tree

Sorting & Searching

• Quick Sort (DIY Implementation)
• Merge Sort (DIY Implementation)
• Binary Search

Stacks & Queues

• Implement Queue using Stacks
• Valid Parentheses

Hashing & Misc

• Missing Number
• Count Distinct (DIY using Set)
• Longest Consecutive Sequence

💡 Tip:
Don’t just memorize – focus on solving, analyzing time/space complexity, and re-solving without looking at solutions. These patterns repeat across companies.