Problems
A curated collection of 23 common Low-Level Design (LLD) interview problems, ranked by probability of being asked in SDE 2 interviews.
Legend:
Very High (80-100%): Must prepare. Asked in almost every LLD round.
High (60-80%): Frequently asked.
Medium (20-60%): Domain-specific or less common.
The Complete Problem List
This section contains detailed solutions and explanations for all 23 problems:
Very High Priority (Must Prepare)
Design Parking Lot - Singleton, Factory, Strategy, Concurrency
Design Rate Limiter - Token Bucket, Thread-Safety, Decorator
Design Tic-Tac-Toe - Game Loop, 2D Arrays, Validation Logic
Design Vending Machine - State Pattern, State Machine, Money Handling
Design Splitwise - Graph Simplification, Strategy (Splits), User/Group
High Priority (Frequently Asked)
Design Snake & Ladder - Game Entity, Observer, Strategy (Dice)
Design Elevator System - State Pattern, Scheduling Algorithms (SCAN/LOOK)
Design Comment System - Materialized Path (Trees), Recursion, Database Design
Design Hotel Management - Booking Factory, Date Concurrency, Singleton
Design Cache (LRU/LFU) - Doubly Linked List + HashMap, Generics
Design Locker Service - Geo-hashing, Locker Size Matching, Inheritance
Medium Priority (Domain-Specific)
Design Coupon System - Composite Pattern, Chain of Responsibility
Design Mentorship Platform - Booking availability, Conflict resolution
Design Logger Library - Chain of Responsibility, Singleton, Sink Strategy
Design Minesweeper - Flood Fill (DFS/BFS), Recursion
Design File System / S3 - Composite Pattern, Metadata vs Data, Permissions
Design Search Engine - Inverted Index, Tries, Tokenization
Design Tetris - Matrix Rotation, Factory Pattern, Game Loop
Design Version Control - Graph (DAG), Hashing (SHA-1), Merkle Tree
Design Tunneling Service - Reverse Proxy, Socket Programming
Design Text Editor - Gap Buffer/Rope, Command Pattern, Undo/Redo
Design Download Manager - Multi-threading, HTTP Ranges, File Merging
Design Unlock Pattern - DFS/Backtracking, Validation Logic
Preparation Strategy
Tier 1 (Fire ): Implement these from scratch 3 times. These are your bread and butter.
Parking Lot, Rate Limiter, Vending Machine, Tic-Tac-Toe, Splitwise.
Tier 2 (Green ): Understand the Class Diagram and Key Design Pattern.
Elevator, Snake & Ladder, Comments, Hotel, LRU Cache.
Tier 3 (Yellow ): Read the code to understand specific algorithms (e.g. QuadTree for Locker, Tries for Search).
Click on any problem above to view its detailed solution and implementation.
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