https://codewitharyan.com/system-design/low-level-design

🔹 Must-Know: Singleton, Factory, Builder, Strategy, Observer, Adapter, Proxy, Decorator, Composite, Flyweight, Template Method, Command, Chain of Responsibility.

🔹 Nice-to-Know (But Rarely Asked): Memento, State, Visitor, Mediator, Interpreter, Bridge.

🔥 FAANG-Level Design Patterns Roadmap

🔥 1. Core OOP Principles (Before Learning Design Patterns)

✅ SOLID Principles (Single Responsibility, Open-Closed, Liskov, Interface Segregation, Dependency Injection)

✅ DRY (Don’t Repeat Yourself) & KISS (Keep It Simple, Stupid)

✅ Composition over Inheritance

✅ Encapsulation, Polymorphism, Abstraction, and Inheritance

Hands-On Practice

✔ Refactor a badly written codebase to follow SOLID principles.

✔ Implement Dependency Injection in Java using Spring Boot.

🔥 2. Creational Design Patterns (Object Creation)

✅ Singleton → Global shared instance (Thread-Safe Singleton, Enum Singleton, Lazy vs Eager Initialization)

✅ Factory Method → Encapsulating Object Creation (Factory Pattern, Abstract Factory)

✅ Builder → Step-by-step object construction (Immutable Objects, Fluent Interface)