Below is a curated list of the most commonly asked Low Level Design (LLD) interview problems.
Each problem includes a short explanation and a link to the complete solution with Java code, UML class diagrams, and detailed walkthroughs.
1. Design Parking Lot System
The system handles parking for different vehicle types such as bikes, cars, and trucks. It manages slot allocation, availability tracking, and entry/exit flow under varying load conditions.
2. Design Elevator / Lift System
The system supports multiple elevators across floors with request handling logic. It focuses on scheduling algorithms to optimize movement and reduce waiting time.
3. Design Movie Ticket Booking System
The system allows users to browse movies, select shows, and book seats. It handles seat locking and ensures consistency during concurrent bookings.
4. Design Snake and Ladder Game
The system simulates a board game with dice rolls, player turns, snakes, and ladders. It manages movement rules and determines winning conditions.
5. Design Hotel Management System
The system manages room inventory, booking, check-in/check-out, and reservation updates across multiple room types.
6. Design Food Delivery System
The system manages restaurants, orders, and delivery assignment. It tracks the full order lifecycle from placement to delivery.
7. Design Library Management System
The system manages books, issuing, returning, and user borrowing history while tracking multiple copies and availability.
8. Design Notification System
The system sends notifications via email, SMS, and push channels. It routes messages based on user preferences and ensures retry mechanisms for failures.
9. Design Real-Time Chat Application
The system enables real-time messaging between users with low latency. It supports one-to-one and group chats with message history and presence tracking.
10. Design Ride Sharing System
The system matches riders with nearby drivers and manages trip lifecycle. It calculates fares dynamically and handles booking and cancellation.
11. Design E-commerce System
The system manages product catalog, cart operations, checkout flow, inventory tracking, and order history.
12. Design Splitwise System
The system handles shared expenses, tracks balances between users, and simplifies debt settlement.
13. Design File Storage System (Google Drive / Dropbox)
The system manages file uploads, folder hierarchy, sharing permissions, and scalable storage retrieval.
14. Design Rate Limiter System
The system controls request traffic and enforces limits per user or service within time windows.
15. Design Airline Reservation System
The system manages flight search, seat booking, and reservations with concurrency-safe booking logic.
16. Design ATM System
The system handles withdrawals, balance checks, authentication, and secure transaction processing.
17. Design Shopping Cart System
The system manages cart items, pricing, updates, and checkout flow with user persistence.
18. Design Social Media Platform
The system supports posts, feeds, likes, comments, and follow relationships at scale.
19. Design Online Bookstore System
The system manages book listings, search, orders, inventory, and recommendations.
20. Design Meeting Scheduler System
The system handles meeting scheduling, participant availability, and conflict resolution.
21. Design Order Inventory Management System
The system manages inventory, stock levels, and ensures orders are placed only when stock is available.
22. Design Customer Issue Resolution System
The system manages customer complaints, ticket workflows, and escalation handling.
23. Design Chess Game
The system simulates chess gameplay with board setup, piece movement rules, check, checkmate, and full game state management.
24. Design Text Editor / Word Processor
The system supports document creation, editing, formatting, versioning, undo/redo, and collaborative-ready architecture.
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Originally published at https://lldcoding.blogspot.com
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