Question 1

What is low-level design in interviews?

Accepted Answer

Low-level design (LLD) interviews evaluate your ability to design the internal structure of a system — classes, interfaces, relationships, and methods. You are typically asked to model a real-world system like a parking lot, elevator, or chess game using object-oriented principles. The focus is on clean abstractions, extensibility, and applying SOLID principles.

Question 2

What design patterns should I know for LLD?

Accepted Answer

The most important design patterns for LLD interviews are Strategy, Observer, Factory, Singleton, and State. You should also be comfortable with Decorator and Builder patterns. Knowing when to apply each pattern — not just how it works — is what separates strong candidates from average ones.

Question 3

How is LLD different from HLD?

Accepted Answer

HLD focuses on the architecture of an entire distributed system — servers, databases, caches, and how they communicate. LLD zooms into a single component or service and asks you to design its internal class hierarchy, data models, and method signatures. Think of HLD as the blueprint of a building and LLD as the detailed floor plan of one room.

Question 4

How should I structure my LLD answer?

Accepted Answer

Begin by clarifying requirements and identifying the core entities (nouns become classes, verbs become methods). Then define class relationships using inheritance and composition, apply relevant design patterns, and walk through a key use case to validate your design. Keeping your code modular and extensible shows the interviewer you think about maintainability.

📐 LLD Foundations

Low-Level Design