Cracking the LLD Interview

🎯 What Even Is Low-Level Design?

Low-Level Design (LLD) is where your big ideas transform into actual code that:

• Builds without errors

• Remains adaptable to change

• Scales gracefully

Think of it as crafting detailed Lego instructions rather than dumping all the bricks in a pile and hoping they fit together.

🎒 Your LLD Survival Kit (Prerequisites)

Before diving deep, ensure you're equipped with the essentials:

• Programming Proficiency: Be comfortable with at least one object-oriented language like Java, C++, or Python.

• Object-Oriented Programming (OOP) Basics

• SOLID Principles

• Design Patterns

• Unified Modeling Language (UML) diagrams

🧱 Object-Oriented Programming (OOP) Basics

OOP is the backbone of LLD. Key concepts include:

• Classes & Objects: Blueprints and their instances.

• Encapsulation: Bundling data with methods.

• Inheritance: Deriving new classes from existing ones.

• Polymorphism: Methods behaving differently based on the object.

🛡️ SOLID Principles

These five principles are your coding superhero team:

1. Single Responsibility Principle (SRP): A class should have only one reason to change.

2. Open/Closed Principle (OCP): Software entities should be open for extension but closed for modification.

3. Liskov Substitution Principle (LSP): Subtypes must be substitutable for their base types.

4. Interface Segregation Principle (ISP): Clients should not be forced to depend on interfaces they do not use.

5. Dependency Inversion Principle (DIP): Depend on abstractions, not on concretions.

🛠️ Handy Design Patterns to Know

Design patterns are tried-and-tested solutions to common problems:

• Factory: Create objects without specifying the exact class.

• Observer: Notify multiple objects about state changes.

• Strategy: Define a family of algorithms and make them interchangeable.

• Decorator: Add responsibilities to objects dynamically.

• Singleton: Ensure a class has only one instance.

📊 UML: Visualizing Your Design

Unified Modeling Language (UML) diagrams are your blueprint for system design:

• Class Diagrams: Show classes and relationships.

• Sequence Diagrams: Detail object interactions over time.

• Activity Diagrams: Represent workflows.

🚀 Ready to Level Up?

This is just the beginning. In the upcoming articles, we'll tackle 20 of the most frequently asked LLD interview questions, dissecting each with clarity and precision.

Stay tuned, and let's crack the LLD interview together!

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