Low-Level Design (LLD)
Master object-oriented design, SOLID principles, and design patterns
What You'll Master
Skills You'll Gain:
- OOP principles and SOLID design principles
- All 23 Gang of Four design patterns with real examples
- Solve real-world problems: Parking Lot, Elevator, Chess, etc.
- Create class diagrams, write clean code, build extensible systems
Key Concepts:
🚀 Learning Path
Learn Principles
Start with OOP and SOLID principles to build a strong foundation.
Master Patterns
Study all 23 design patterns with examples and use cases.
Apply to Real Systems
Practice with real-world case studies like Parking Lot and Elevator.
📖 All Modules
Welcome
3 topicsLLD Introduction
4 topicsOOP Fundamentals
8 topicsClasses and Objects
Building blocks of OOP
Enums
Enumeration types in OOP
Interfaces
Contracts for classes
Encapsulation
Data hiding and bundling
Abstraction
Hiding implementation details
Inheritance
Code reuse through parent-child relationships
Polymorphism
Many forms of the same entity
Quiz
Test your OOP knowledge
Class Relationships
6 topicsDesign Principles
8 topicsDRY Principle
Don't Repeat Yourself
KISS Principle
Keep It Simple, Stupid
YAGNI Principle
You Aren't Gonna Need It
Law of Demeter
Principle of least knowledge
Separation of Concerns
Divide program into distinct features
Coupling and Cohesion
Measuring module dependencies and focus
Composing Objects Principle
Favor composition over inheritance
Quiz
Test your design principles knowledge
SOLID Principles
6 topicsSingle Responsibility Principle
A class should have one reason to change
Open/Closed Principle
Open for extension, closed for modification
Liskov Substitution Principle
Subtypes must be substitutable for base types
Interface Segregation Principle
Many client-specific interfaces over one general interface
Dependency Inversion Principle
Depend on abstractions, not concretions
Quiz
Test your SOLID principles knowledge
UML
5 topicsDesign Patterns Introduction
2 topicsCreational Patterns
6 topicsStructural Patterns
8 topicsAdapter
Make incompatible interfaces work together
Facade
Provide simplified interface to complex subsystem
Decorator
Add new functionality to objects dynamically
Composite
Compose objects into tree structures
Proxy
Provide surrogate or placeholder for another object
Bridge
Separate abstraction from implementation
Flyweight
Share common state between multiple objects
Quiz
Test your structural patterns knowledge
Behavioral Patterns
11 topicsStrategy
Define family of algorithms and make them interchangeable
Iterator
Access elements sequentially without exposing structure
Observer
Define one-to-many dependency between objects
Command
Encapsulate request as an object
State
Allow object to change behavior when state changes
Template Method
Define skeleton of algorithm in base class
Chain of Responsibility
Pass request along chain of handlers
Visitor
Separate algorithms from objects they operate on
Mediator
Reduce coupling between communicating objects
Memento
Capture and restore object state
Quiz
Test your behavioral patterns knowledge
Additional Patterns
9 topicsNull Object Pattern
Provide default behavior for null references
Repository Pattern
Mediate between domain and data mapping layers
MVC Pattern
Model-View-Controller architecture
Dependency Injection Pattern
Inject dependencies rather than creating them
Specification Pattern
Encapsulate business rules as reusable objects
Game Loop Pattern
Decouple game time from user input and processor speed
Thread Pool Pattern
Manage and reuse threads efficiently
Producer Consumer Pattern
Separate production and consumption of data
Quiz
Test your additional patterns knowledge
LLD Interview Tips
3 topicsLLD Interview Questions
36 topicsDesign LRU Cache
Implement Least Recently Used cache
Design Parking Lot
Design a multi-level parking lot system
Design Notification System
Build a notification delivery system
Design Rate Limiter
Implement request rate limiting
Design Elevator System
Design an elevator control system
Design BookMyShow
Movie ticket booking system
Design Chess Game
Design a chess game with all rules
Design ATM System
Design an automated teller machine
Design Library Management
System for managing library operations
Design Food Delivery App
Like Uber Eats or DoorDash
Design Message Queue
Implement a message queue system
Design Vending Machine
Product dispensing machine
Design Hotel Booking System
Room reservation and management
Design Online Shopping Cart
E-commerce shopping cart system
Design File System
In-memory file system with directories
Design Snake and Ladder
Classic board game implementation
Design Tic-Tac-Toe
N x N board game
Design Splitwise
Expense sharing application
Design Car Rental System
Vehicle rental management
Design Logging Framework
Multi-level logging system
Design Cricinfo
Cricket score tracking system
Design Task Scheduler
Schedule and execute tasks
Design Meeting Scheduler
Calendar and room booking system
Design Uber/Ride Sharing
Ride matching and routing
Design Social Network
Like Facebook or Twitter
Design Search Autocomplete
Type-ahead search suggestions
Design Stock Exchange
Order matching system
Design Airline Management
Flight and reservation system
Design Music Streaming
Like Spotify or Apple Music
Design Payment Gateway
Process online payments
Design Blockchain
Distributed ledger system
Design Load Balancer
Distribute traffic across servers
Design API Gateway
API request routing and management
Design Distributed Cache
Multi-node caching system
Design Trading Platform
Real-time stock trading system
Design Video Streaming
Like YouTube or Netflix
💡 Interview Success Tips
LLD interviews test your ability to design clean, maintainable, and extensible systems.
- ✓ Always start by clarifying requirements and constraints
- ✓ Identify core entities, their attributes, and relationships
- ✓ Apply SOLID principles to make your design flexible
- ✓ Use appropriate design patterns to solve common problems
- ✓ Draw clear UML diagrams to communicate your design