🚀 50 Low-Level Design (LLD) Problems Solved Using Java !

@code-with-Bharadwaj

A complete, interview-ready Low-Level Design master repository built with clean Java and real-world system thinking.

About • Highlights • Problems • Structure • Principles • How To Use • Roadmap • Author

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📌 About This Repository

This repository contains 50+ carefully selected Low-Level Design (LLD) problems, implemented using pure Java with strong Object-Oriented Design principles.

It is built specifically for

	Purpose
🧠	LLD & System Design interviews
🎯	SDE-1 / SDE-2 / SDE-3 / Backend roles
📹	YouTube-based LLD teaching & explanations
🏗️	Learning real-world, scalable software design

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🔥 What Makes This Repo Awesome !

• ✅ 50+ most frequently asked LLD interview problems
• ✅ Clean, modular & extensible Java architecture
• ✅ Real-world constraints & production-style thinking
• ✅ Covers Concurrency, Caching, Distributed Systems, Games
• ✅ Perfect for FAANG & top product-based companies

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🧩 Complete List of LLD Problems !

Category	Problems
🏦 Finance & Banking	ATM System · Bank Account Management System · Digital Wallet System · Auction System
🚗 Rental & Booking	Car Rental System · Event Booking System · Hotel Management System
🛒 E-Commerce & Business	Shopping Cart System · Food Delivery System · Restaurant Management System · Recommendation System
⚙️ Cache, Storage & Data	LRU Cache · LFU Cache · Redis-like Cache · Key-Value Store · File System · Library Management System
🌐 Distributed & Backend Systems	Distributed Lock System · Message Queue · Rate Limited API Gateway · Log Aggregation System · Metrics Monitoring System · Background Job Processor · Web Crawler · URL Shortener
🧵 Concurrency & Scheduling	Thread Pool · Producer Consumer System · Task Scheduler · Session Management System
🎮 Games & Simulations	Chess Game · Chess Tournament System · Tic Tac Toe Game · Snake and Ladder Game · Traffic Light System · Elevator System · Vending Machine
🔐 Utilities & Engines	Feature Flag System · Notification Preference Engine · Search Autocomplete System · Game Player Lobby System

📋 Expand the detailed list

🏦 Finance & Banking

• ATM System
• Bank Account Management System
• Digital Wallet System
• Auction System

🚗 Rental & Booking

• Car Rental System
• Event Booking System
• Hotel Management System

🛒 E-Commerce & Business

• Shopping Cart System
• Food Delivery System
• Restaurant Management System
• Recommendation System

⚙️ Cache, Storage & Data

• LRU Cache
• LFU Cache
• Redis-like Cache
• Key-Value Store
• File System
• Library Management System

🌐 Distributed & Backend Systems

• Distributed Lock System
• Message Queue
• Rate Limited API Gateway
• Log Aggregation System
• Metrics Monitoring System
• Background Job Processor
• Web Crawler
• URL Shortener

🧵 Concurrency & Scheduling

• Thread Pool
• Producer Consumer System
• Task Scheduler
• Session Management System

🎮 Games & Simulations

• Chess Game
• Chess Tournament System
• Tic Tac Toe Game
• Snake and Ladder Game
• Traffic Light System
• Elevator System
• Vending Machine

🔐 Utilities & Engines

• Feature Flag System
• Notification Preference Engine
• Search Autocomplete System
• Game Player Lobby System

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📁 Full Project Structure

src/main/java/org/example/
│
├── ATMSystem
├── AuctionSystem
├── BackgroundJobProcessor
├── BankAccountManagementSystem
├── CarRentalSystem
├── ChessGame
├── ChessTournamentSystem
├── DigitalWalletSystem
├── DistributedLockSystem
├── ElevatorSystem
├── EventBookingSystem
├── FeatureFlagSystem
├── FileSystem
├── FoodDeliverySystem
├── GamePlayerLobbySystem
├── HotelManagementSystem
├── KeyValueStore
├── LFUCache
├── LRUCache
├── LibraryManagementSystem
├── LogAggregationSystem
├── MessageQueue
├── MetricsMonitoringSystem
├── NotificationPreferenceEngine
├── ProducerConsumerSystem
├── RateLimitedAPIGateway
├── RecommendationSystem
├── RedisLikeCache
├── RestaurantManagementSystem
├── SearchAutocompleteSystem
├── SessionManagementSystem
├── ShoppingCartSystem
├── SnakeAndLadder
├── TaskScheduler
├── ThreadPool
├── TicTacToeGame
├── TrafficLightSystem
├── URLShortener
├── VendingMachine
└── WebCrawler

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🧠 Design Principles Used

	Principle
🧱	SOLID Principles
🎯	Clean Object-Oriented Design
✂️	Separation of Concerns
🔗	Loose Coupling & High Cohesion
🔧	Extensible & Maintainable Systems
💼	Interview-friendly structure

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🎯 Who Should Use This?

• 👨‍💻 Backend / Java Developers
• 🎓 Engineers preparing for LLD interviews
• 📹 YouTubers & Educators teaching System Design
• 📚 Students learning OOP & LLD
• 🏆 Anyone serious about software design fundamentals

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🛠️ Tech Stack

Language	Java
Paradigm	Object-Oriented Programming
Focus	Low-Level Design (LLD)
Goal	Interview-ready & production-style design

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⭐ How To Use This Repository

Step	Action
1	📥 Clone the repository
2	🎯 Choose any system (e.g., LRUCache, ATMSystem)
3	🔍 Understand class responsibilities & interactions
4	🧩 Extend features (thread-safety, scaling, persistence)
5	🎤 Practice explaining it like an interview

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📈 Future Roadmap

• UML diagrams for every system
• Thread-safe enhancements
• Design pattern mapping
• Unit & integration tests
• Time & space complexity notes

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🤝 Contributions

Contributions are welcome!

• 🛠 Improve designs
• 📐 Add UML diagrams
• ⚡ Optimize implementations
• 📝 Enhance documentation

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🔗 Author

Bharadwaj

 

If this repository helps you:

• ⭐ Star it
• 🔁 Share it
• 📢 Recommend it to fellow LLD learners

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🏁 Final Note

"Low-Level Design is not about writing more code, it's about designing the right abstractions."

Happy Designing 🚀