01-LLD-Questions

Low-Level Design (LLD) Interview Questions

This directory contains comprehensive LLD interview questions organized by design patterns and problem types.

📁 Directory Structure

• Creational Patterns - Singleton, Factory, Builder, etc.
• Structural Patterns - Adapter, Decorator, Facade, etc.
• Behavioral Patterns - Observer, Strategy, State, etc.
• Classical Problems - Parking Lot, ATM, Elevator, etc.
• Real-World Systems - E-commerce, Social Media, etc.

🎯 What Interviewers Look For

1. Object-Oriented Thinking: Ability to model real-world entities as classes
2. Design Pattern Knowledge: Understanding when and how to apply patterns
3. SOLID Principles: Writing maintainable, extensible code
4. Edge Case Handling: Considering boundary conditions
5. Code Organization: Clean, readable, well-structured code
6. Communication: Explaining design decisions clearly

📚 Prerequisites

Before diving into questions, ensure you understand:

• OOP Fundamentals
• SOLID Principles
• Design Patterns Overview
• UML Basics

🚀 How to Approach LLD Problems

1. Clarify Requirements: Ask questions about scope, constraints, and edge cases
2. Identify Entities: Find nouns in the problem statement (classes)
3. Define Relationships: Establish associations, aggregations, compositions
4. Apply Patterns: Use appropriate design patterns where needed
5. Design Methods: Define clear APIs and responsibilities
6. Handle Edge Cases: Consider error scenarios and boundary conditions
7. Draw Diagrams: Create class diagrams to visualize relationships

📖 Question Format

Each question includes:

• Problem Statement: Clear description of what to design
• Why This Question: Relevance to interviews and real-world scenarios
• Design Pattern: Which pattern(s) apply and why
• Key Entities: Main classes and their responsibilities
• Approach: Step-by-step design process
• Edge Cases: Important scenarios to consider

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Navigate to specific categories to start practicing!