Improve README with LLD course details

README.md

@@ -3,3 +3,267 @@ All Codes and Notes for System Design (LLD) Playlist of Coder Army.
 Absolutely Free on Coder Army Youtube Channel. 
 
 Playlist Link : https://youtube.com/playlist?list=PLQEaRBV9gAFvzp6XhcNFpk1WdOcyVo9qT&si=Ihevlxfa3nczoXp0
+
+# 🧠 Low Level Design (LLD) – Complete Course (From Basics to Advanced)
+
+A **comprehensive Low Level Design (LLD) course** covering **Object-Oriented Programming, Design Principles, UML Diagrams, Design Patterns, and Real-World Case Studies** with clean explanations and code examples.
+
+This course is designed for:
+- 💻 Software Engineering Interviews
+- 🚀 Backend / Full Stack Developers
+- 🏗️ System Design Preparation (LLD part)
+- 📚 Strong OOP & Design Foundation
+
+---
+
+## 📌 What You Will Learn
+
+- Core **Object-Oriented Programming (OOP)** concepts
+- **SOLID principles** with real-world examples
+- **UML diagrams** (Class, Sequence, Use Case, etc.)
+- **Design Patterns** (Creational, Structural, Behavioral)
+- **Clean Code & Best Practices**
+- **Real-world LLD Case Studies**
+- Interview-oriented problem solving
+
+---
+
+## 📂 Course Structure
+
+### 1️⃣ Object-Oriented Programming (OOP)
+
+- What is OOP?
+- Procedural vs Object-Oriented Programming
+- Classes & Objects
+- Encapsulation
+- Abstraction
+- Inheritance
+- Polymorphism
+- Interfaces vs Abstract Classes
+- Composition vs Inheritance
+- Association, Aggregation, Composition
+- Method Overloading & Overriding
+- Access Modifiers
+- Constructor & Destructor
+- Static Members
+- Immutability
+
+---
+
+### 2️⃣ Object-Oriented Analysis & Design (OOAD)
+
+- What is OOAD?
+- Requirement Analysis
+- Identifying Objects
+- Identifying Responsibilities
+- Use Case Analysis
+- Domain Modeling
+- CRC Cards (Class-Responsibility-Collaboration)
+
+---
+
+### 3️⃣ UML Diagrams (Unified Modeling Language)
+
+- Introduction to UML
+- Class Diagram
+- Object Diagram
+- Use Case Diagram
+- Sequence Diagram
+- Activity Diagram
+- State Diagram
+- Component Diagram
+- Deployment Diagram
+- Relationships in UML
+- Multiplicity & Notations
+
+---
+
+### 4️⃣ SOLID Design Principles
+
+- **S** – Single Responsibility Principle (SRP)
+- **O** – Open/Closed Principle (OCP)
+- **L** – Liskov Substitution Principle (LSP)
+- **I** – Interface Segregation Principle (ISP)
+- **D** – Dependency Inversion Principle (DIP)
+- Violations & Fixes with examples
+
+---
+
+### 5️⃣ Other Important Design Principles
+
+- DRY (Don’t Repeat Yourself)
+- KISS (Keep It Simple, Stupid)
+- YAGNI (You Aren’t Gonna Need It)
+- Separation of Concerns
+- High Cohesion & Low Coupling
+- Law of Demeter
+- Favor Composition over Inheritance
+
+---
+
+### 6️⃣ Design Patterns – Introduction
+
+- What are Design Patterns?
+- When to use Design Patterns?
+- Advantages & Disadvantages
+- Pattern Categories:
+  - Creational
+  - Structural
+  - Behavioral
+
+---
+
+### 7️⃣ Creational Design Patterns
+
+- Singleton
+- Factory
+- Abstract Factory
+- Builder
+- Prototype
+- Object Pool
+
+---
+
+### 8️⃣ Structural Design Patterns
+
+- Adapter
+- Bridge
+- Composite
+- Decorator
+- Facade
+- Flyweight
+- Proxy
+
+---
+
+### 9️⃣ Behavioral Design Patterns
+
+- Strategy
+- Observer
+- Command
+- Iterator
+- State
+- Template Method
+- Chain of Responsibility
+- Mediator
+- Memento
+- Visitor
+
+---
+
+### 🔟 Concurrency & Thread Safety (LLD Perspective)
+
+- Basics of Multithreading
+- Synchronization
+- Locks & Mutex
+- Deadlock, Livelock, Starvation
+- Thread-safe Design
+- Singleton Thread Safety
+
+---
+
+### 1️⃣1️⃣ Exception Handling & Logging Design
+
+- Designing Custom Exceptions
+- Global Exception Handling
+- Logging Levels
+- Logging Best Practices
+- Error Codes vs Exceptions
+
+---
+
+### 1️⃣2️⃣ API & Module Design
+
+- Designing Clean APIs
+- RESTful Design Basics
+- DTOs vs Entities
+- Validation Layer
+- Service Layer Design
+- Repository Pattern
+
+---
+
+### 1️⃣3️⃣ Database Design (LLD Level)
+
+- Entity Modeling
+- Relationships
+- Normalization
+- Indexing Basics
+- Designing Tables from Class Diagrams
+
+---
+
+### 1️⃣4️⃣ Real-World LLD Case Studies
+
+- Design a Parking Lot System
+- Design a Library Management System
+- Design an Elevator System
+- Design a Food Delivery App
+- Design a Movie Ticket Booking System
+- Design a Ride Sharing System
+- Design a URL Shortener (LLD)
+- Design a Cache System
+- Design a Notification System
+
+---
+
+### 1️⃣5️⃣ Interview Preparation
+
+- How to approach LLD problems
+- Step-by-step LLD solution framework
+- Common interview mistakes
+- LLD Interview Questions
+- Mock LLD Problems with solutions
+
+---
+
+## 🛠️ Tech Stack Used
+
+- Language: Java / C++ / Python (examples)
+- UML Tools: Draw.io / Lucidchart
+- IDE: VS Code / IntelliJ
+
+---
+
+## 📈 Who Should Use This Course?
+
+- Beginners learning OOP
+- Intermediate developers improving design skills
+- Final-year students
+- Interview candidates
+- Backend / Full Stack Developers
+
+---
+
+## 🤝 Contributing
+
+Contributions are welcome! 🎉  
+
+Steps:
+1. Fork the repository
+2. Create a feature branch
+3. Make changes
+4. Commit & push
+5. Create a Pull Request
+
+---
+
+## ⭐ Support
+
+If this repository helps you:
+- ⭐ Star the repo
+- 🍴 Fork it
+- 📢 Share with others
+
+---
+
+## 📬 Contact
+
+Created with ❤️ for developers.  
+For suggestions or improvements, feel free to open an issue or PR.
+
+---
+
+## 📜 License
+
+This project is licensed under the **MIT License**.