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Bharadwaj

🚀 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

📌 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

🔥 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

🧩 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

📁 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

🧠 Design Principles Used

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

🎯 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

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

⭐ 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

📈 Future Roadmap

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

🤝 Contributions

Contributions are welcome!

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

🔗 Author

Bharadwaj

 

If this repository helps you:

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

🏁 Final Note

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

Happy Designing 🚀