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🏗️ Low Level Design (LLD) Collection

A comprehensive collection of production-grade Low Level Design (LLD) implementations in Java. This repository serves as a reference for clean code, SOLID principles, and common architectural patterns used in building robust, scalable systems.

📂 Project Index

This repository contains multiple versions and variations of common LLD problems, including simplified "standard" versions and more advanced "coaching" implementations.

Core Projects

Project Key Patterns Documentation
Amazon Locker System Strategy, State, Facade Standard | Advanced
Chess Game Strategy, Template Method, Facade Detailed Design
Coffee Shop Decorator, Builder, Validator Detailed Design
Elevator System State Machine, Dispatcher, Singleton Standard | Advanced
LRU Cache Doubly Linked List + HashMap Detailed Design
Parking Lot Strategy, Factory, State Standard | Advanced
Rate Limiter Strategy, Token Bucket, Fixed Window Detailed Design
SplitWise Strategy, Balance Sheet, Greedy Settlement Detailed Design
Unix FIND Composite, Chain of Responsibility Detailed Design

🧠 Design Principles Applied

Across all implementations, the following principles are strictly followed to ensure maintainability and extensibility:

Principle Description
SOLID Ensuring single responsibility, open/closed designs, and interface segregation.
Strategy Pattern Used for swappable algorithms (e.g., pricing, allocation, rate limiting).
Facade Pattern Providing simple interfaces to complex subsystems (e.g., LockerSystem, ElevatorController).
State Pattern Managing complex object lifecycles (e.g., Elevator status, Locker availability).
Composite Pattern Building hierarchical structures (e.g., Unix Find filters).

🚀 Getting Started

Each project is located in its own directory and can be explored independently.

Running a Project

Most projects are standard Java or Maven-based. To run a project:

  1. Navigate to the directory:

    cd <Project_Directory>

  2. Run via Maven (if applicable):

    mvn compile exec:java -Dexec.mainClass="org.example.Main"

  3. Or run the Driver or Main class directly using your IDE (IntelliJ IDEA, Eclipse, etc.).

🛠️ Tech Stack

  • Language: Java 17+
  • Build Tool: Maven (where applicable)
  • Design Philosophy: Object-Oriented Design (OOD)
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