🌀 Low Level Design

UML Class Diagram Basics

📌 Table Of Contents

1. SOLID Principles

1. Single Responsibility Principle (SRP)

2. Open Closed Principle (OCP)

3. Liskov Substitution Principle (LSP)

4. Interface Segregation Principle (ISP)

5. Dependency Inversion Principle (DIP)

2. Design Patterns

2.1 Creational Patterns

1. Singleton Design Pattern

2. Factory Design Pattern

3. Abstract Factory Pattern

4. Builder Design Pattern

5. Prototype Design Pattern

2.2 Structural Patterns

1. Adapter Design Pattern

2. Decorator Design Pattern

3. Facade Design Pattern

4. Proxy Design Pattern

5. Composite Design Pattern

6. Bridge Design Pattern

7. Flyweight Design Pattern

2.3 Behavioral Patterns

1. Strategy Design Pattern

2. Observer Design Pattern

3. Command Design Pattern

4. State Design Pattern

5. Chain of Responsibility Pattern

6. Template Method Pattern

7. Mediator Design Pattern

8. Visitor Design Pattern

9. Iterator Design Pattern

3. Real LLD Problems

1. Parking Lot System Design

2. BookMyShow LLD

3. Elevator System Design

4. ATM Machine Design

5. Hotel Management System

6. Food Delivery System Design

7. Cab Booking System Design

8. Splitwise LLD

9. Chess Game Design

10. Snake and Ladder Design

11. Tic Tac Toe Design

12. Logger Rate Limiter Design

13. Notification System Design

14. Cache System Design

15. File System Design

16. API Rate Limiter Design

17. Vending Machine Design

18. Cricbuzz System Design

🎯 Suggested Study Order

Phase 1 — Core Fundamentals

• SOLID Principles
• Dependency Injection
• Inversion of Control
• UML Basics

Phase 2 — Creational Patterns

• Singleton
• Factory
• Abstract Factory
• Builder
• Prototype

Phase 3 — Structural Patterns

• Adapter
• Decorator
• Facade
• Proxy
• Composite
• Bridge
• Flyweight

Phase 4 — Behavioral Patterns

• Strategy
• Observer
• Command
• State
• Chain of Responsibility
• Template Method
• Mediator
• Visitor
• Iterator

Phase 5 — Real LLD Problems

• Parking Lot
• BookMyShow
• Elevator
• ATM
• Splitwise
• Cab Booking
• Food Delivery
• Chess
• Notification System

🚀 Interview Preparation Strategy

Step 1

Learn:

• SOLID
• OOP
• UML

Step 2

Master:

• Strategy
• Factory
• Observer
• Decorator

These appear everywhere in LLD interviews.

Step 3

Solve 10–15 real systems:

• Parking Lot
• ATM
• Splitwise
• BookMyShow

Step 4

For every problem:

• Draw UML
• Explain responsibilities
• Identify SOLID principles
• Explain extensibility
• Discuss tradeoffs

Source Playlist:
YouTube Playlist