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PREMIUM GUIDE

DSA Interview Prep: 100 Must-Solve Problems

Curated list of 100 problems that cover 90% of coding interviews — with patterns, approaches & time targets

4-8 weeks Intermediate 4 Sections +100 XP

Arrays & Strings (25 problems)

Section 1 of 4

1.1

Pattern: Two Pointers — Used in: Container with most water, 3Sum, Remove duplicates. Time target: 15-20 min each.

1.2

Pattern: Sliding Window — Used in: Maximum subarray, Longest substring without repeating chars. Key: expand right, shrink left.

1.3

Pattern: Prefix Sum — Used in: Subarray sum equals K, Range sum query. Pre-compute cumulative sums for O(1) range queries.

1.4

Must-solve: Two Sum, Best Time to Buy/Sell Stock, Product of Array Except Self, Merge Intervals, Group Anagrams.

Practice Exercise

Solve these 5 on LeetCode today: Two Sum, Valid Anagram, Maximum Subarray, Merge Intervals, 3Sum. Time yourself.

Trees & Graphs (25 problems)

Section 2 of 4

2.1

Binary Trees: Traversals (inorder, preorder, postorder), Max depth, Validate BST, Lowest Common Ancestor.

2.2

Graphs: BFS for shortest path, DFS for connectivity, Topological sort for dependencies, Dijkstra for weighted shortest path.

2.3

Pattern: Level-order traversal using queue. Pattern: Recursive DFS with base case + recursive case.

2.4

Must-solve: Invert Binary Tree, Same Tree, Number of Islands, Course Schedule, Word Ladder.

Dynamic Programming (25 problems)

Section 3 of 4

3.1

DP = Recursion + Memoization. If a problem has overlapping subproblems and optimal substructure → use DP.

3.2

Pattern: 1D DP — Climbing stairs, House robber, Coin change. Start with recursive solution, then add memo table.

3.3

Pattern: 2D DP — Longest common subsequence, Edit distance, Unique paths. Build a 2D table, fill row by row.

3.4

Must-solve: Climbing Stairs, Coin Change, Longest Increasing Subsequence, 0/1 Knapsack, Edit Distance.

System Design Basics (for SDE-2+)

Section 4 of 4

4.1

Framework: Requirements → Estimation → API Design → Database Schema → High-Level Architecture → Deep Dive → Bottlenecks.

4.2

Must-know concepts: Load balancing, Caching (Redis), Database sharding, Message queues (Kafka), CDN, Microservices.

4.3

Common questions: Design URL shortener, Design Twitter feed, Design WhatsApp, Design parking lot (LLD).

4.4

Resources: "System Design Interview" by Alex Xu, Gaurav Sen YouTube, ByteByteGo newsletter.

Unlock Full Guide

3 more sections with exercises, tips & next steps