What is an OOD Interview?

What is a Low Level Design / OOD Interview?

A Low Level Design (LLD) interview, also called a Machine Coding or Object-Oriented Design (OOD) interview, tests your ability to translate real-world systems into clean, extensible code.

What the interviewer is looking for

1. Requirements clarification — Do you ask the right questions before diving into code?
2. Entity identification — Can you identify the key objects/classes in a system?
3. Class design — Are your classes cohesive? Single responsibility?
4. Relationships — Do you correctly model inheritance, composition, associations?
5. Design patterns — Do you recognize and apply appropriate patterns?
6. Code quality — Is your code readable, extensible, and correct?
7. Edge cases — Do you handle null cases, concurrent access, invalid inputs?

The 45-minute framework

| Time | Activity | |------|----------| | 0–5 min | Clarify requirements, define scope | | 5–10 min | Identify entities and relationships | | 10–15 min | Define class interfaces and relationships (class diagram) | | 15–40 min | Implement core classes and behaviors | | 40–45 min | Test cases, walk through scenarios |

What NOT to do

• Don't start coding immediately — clarify requirements first
• Don't design for every possible future requirement
• Don't over-engineer — a working solution beats a perfect design
• Don't forget to mention design patterns you're using and why

Practice on this platform

Each problem here follows the real interview structure:

1. Problem statement — What the system needs to do
2. Constraints — Boundaries and rules
3. Design hints — Progressive hints using the guided approach
4. Code editor — Write your solution
5. Test cases — Validate core behaviors
6. Reference solution — See the ideal approach with explanations