Low-Level Design Interview Preparation

A comprehensive repository containing popular Design Patterns, SOLID principles, and common Low-Level Design (LLD) problems implemented in both Java and Golang. This repository is specifically designed for interview preparation and learning software design principles.

🎯 What This Repository Contains

🏗️ Design Patterns

Learn and practice essential design patterns with complete implementations:

• Abstract Factory Pattern - Creating families of related objects
• Builder Pattern - Step-by-step object construction
• Decorator Pattern - Adding behavior dynamically
• Factory Pattern - Object creation without specifying exact classes
• Observer Pattern - Event-driven communication between objects
• Singleton Pattern - Ensuring single instance of a class
• Strategy Pattern - Interchangeable algorithms

🔧 SOLID Principles

Master the fundamental principles of object-oriented design:

• Single Responsibility Principle (SRP) - One class, one responsibility
• Open/Closed Principle (OCP) - Open for extension, closed for modification
• Liskov Substitution Principle (LSP) - Subtypes are substitutable for base types
• Interface Segregation Principle (ISP) - Many specific interfaces over one general interface
• Dependency Inversion Principle (DIP) - Depend on abstractions, not concretions

🎮 Common LLD Problems

Practice with real-world system design problems:

• Food Delivery System - Restaurant management, order processing, delivery
• LRU Cache - Least Recently Used cache implementation
• Parking Lot System - Vehicle parking with different spot types
• Snakes and Ladders - Board game with jumpers and dice
• Tic Tac Toe - Classic game with game state management
• Vending Machine - Product dispensing with payment processing

🚀 Getting Started

Prerequisites

For Java Examples:

• Java 17 or higher
• Maven 3.6 or higher (for some examples)

For Golang Examples:

• Go 1.19 or higher

Running Examples

Java Examples:

# Navigate to specific pattern/problem
cd "Design Patterns/Factory Design Pattern/Java"

# run
java Main.java

Golang Examples:

# Navigate to specific pattern/problem
cd "Design Patterns/Factory Design Pattern/Golang"

# run
go run main.go

🎓 Learning Path

1. Start with SOLID Principles

Begin with the foundational principles that guide good software design:

• Single Responsibility Principle
• Open/Closed Principle
• Liskov Substitution Principle
• Interface Segregation Principle
• Dependency Inversion Principle

2. Learn Design Patterns

Move to design patterns that solve common design problems:

• Creational Patterns: Factory, Abstract Factory, Builder, Singleton
• Structural Patterns: Decorator
• Behavioral Patterns: Observer, Strategy

3. Practice with LLD Problems

Apply your knowledge to real-world scenarios:

• Start with simpler problems like Tic Tac Toe
• Progress to complex systems like Food Delivery
• Focus on object modeling and interaction design

💡 Key Concepts Covered

Design Patterns

• When to use each pattern
• Implementation details in multiple languages
• Real-world applications and examples
• Benefits and drawbacks of each pattern

SOLID Principles

• Practical examples of violations and solutions
• Code refactoring techniques
• Best practices for maintainable code
• Common pitfalls and how to avoid them

System Design

• Object modeling and relationships
• Class responsibility assignment
• Interface design and abstraction
• Error handling and edge cases

🔍 Interview Tips

For Design Pattern Questions:

• Understand the problem each pattern solves
• Know when to use vs. when not to use
• Be able to implement from scratch
• Explain trade-offs and alternatives

For SOLID Principle Questions:

• Identify violations in given code
• Suggest refactoring approaches
• Explain benefits of following principles
• Provide real-world examples

For LLD Problem Questions:

• Start with core entities and their relationships
• Design clean interfaces and abstractions
• Consider scalability and extensibility
• Handle edge cases and error scenarios

🤝 Contributing

Feel free to contribute to this repository by:

• Adding new design patterns
• Improving existing implementations
• Adding more LLD problems
• Enhancing documentation
• Providing better examples

📄 License

This project is open source and available under the MIT License.

🙏 Acknowledgments

This repository is created for the developer community to prepare for technical interviews and improve software design skills. Feel free to star, fork, and share!

🌟 Special Thanks To

• Open Source Community - For inspiring the creation of educational resources
• Interviewers & Candidates - Whose questions and experiences shaped this content
• Design Pattern Pioneers - Gang of Four (GoF) and other software design visionaries
• SOLID Principles Authors - Robert C. Martin and other thought leaders in clean code
• Contributors - Everyone who has helped improve this repository

📚 Resources That Inspired This Repository

• "Design Patterns: Elements of Reusable Object-Oriented Software" by GoF
• "Clean Code" by Robert C. Martin
• "Head First Design Patterns" by Freeman & Robson
• Various technical interview preparation materials and courses

💪 Community Support

• GitHub Stars - Your appreciation motivates continued development
• Issue Reports - Helping identify areas for improvement
• Pull Requests - Community contributions that make this better
• Discussions - Sharing knowledge and experiences

🎯 Future Goals

• Add more design patterns (Adapter, Facade, Command, etc.)
• Include more programming languages (Python, C++, JavaScript)
• Create interactive examples and exercises
• Build a community-driven learning platform

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Happy Learning and Good Luck with Your Interviews! 🚀