Machine Coding vs LLD: What's the Difference?

Machine Coding and LLD are often confused because both involve designing classes and writing code.

But the way you approach the two interviews is quite different.

What Is LLD?

LLD stands for Low-Level Design.

LLD is usually a more open-ended discussion where you work with the interviewer to define the problem before designing the solution.

For example, the interviewer might say:

"Design BookMyShow."

They won't necessarily give you a detailed list of requirements or functions.

Your first step is to discuss the requirements with the interviewer and agree on what functionality you are going to build.

You clarify questions like:

• What features do we need?
• What functionality are we going to support?
• What is in scope for this interview?
• What is out of scope?

For example, you might agree to build:

Search for a movie
View available shows
Select seats
Book seats
Make payment
Cancel a booking

Once you and the interviewer are aligned on what you're going to build, you start designing the solution.

A good way to approach LLD is bottom-up.

You start with the core entities and gradually build towards the APIs and overall application design.

1. Identify the Core Entities

First, identify the main entities in the system:

Movie
Theatre
Screen
Show
Seat
Booking
Payment
User

Then think about the relationships between these entities and the responsibilities each one should have.

2. Define Interfaces, Abstract Classes & Concrete Classes

Next, decide how these entities should be represented in code.

Think about:

• What should be an interface?
• What should be an abstract class?
• What should be a concrete class?
• What methods and responsibilities should each class have?
• How should the classes interact with each other?

3. Design the DAO / Repository & Data Layer

Once the core objects are clear, think about how the data will be persisted.

You may need to discuss:

What tables do we need?
What should the schema look like?
What relationships should exist?
Which columns need indexes?
What queries will be frequent?
Which data store should we use?

For example, if the interviewer asks:

"How would you efficiently find available seats for a show?"

You may need to think about the table structure, indexes, query patterns, and data-store strategy.

4. Design the Internal Logic & Patterns

Now design how the internal components work together.

This is where you may use design patterns such as:

• Strategy Pattern — when behavior can vary
• Factory Pattern — when object creation needs to be controlled

The goal is to keep the design clean, extensible, and easy to change when new requirements are introduced.

5. Design Controllers & APIs

Finally, think about how the system will be exposed to the outside world.

You decide:

• What controllers do we need?
• What APIs should we expose?
• What should each API accept and return?
• When should we use GET, POST, PUT, DELETE, etc.?
• What should the API and method signatures look like?

During this discussion, the interviewer may introduce new requirements:

"What if we add different types of seats?"

"What if we add another payment method?"

"What if a booking expires?"

You need to adapt your design as the requirements evolve.

That's what makes LLD open-ended and discussion-driven.

What Is Machine Coding?

Machine Coding is generally more implementation-focused — as introduced in What is Machine Coding?.

Instead of asking you to figure out the entire problem from a broad statement, the interviewer typically gives you a more concrete problem and expected functionality — the exact questions format covered in that chapter.

For example:

"Build a Parking Lot system."

You may be given requirements such as:

• Park a vehicle
• Unpark a vehicle
• Generate a ticket
• Find available spots
• Calculate parking fees
• Support different vehicle types

Now your primary job is to build the system.

You need to:

1. Understand the given requirements
2. Design the classes
3. Define the necessary interfaces
4. Implement the functionality
5. Handle edge cases
6. Test the application
7. Refactor if time allows

The emphasis is less on discovering the entire problem and more on turning the given requirements into working software.

LLD vs Machine Coding

How Should You Prepare for Both Rounds?

Since LLD and Machine Coding test different skills, your preparation should be slightly different too.

For LLD

For LLD, go deeper into design and discussion.

Focus more on:

• Requirement clarification — learn to ask the right questions and close the scope
• UML and class diagrams — practice visualizing and explaining your design
• Bottom-up design — move from entities and classes to data layer, internal design, controllers, and APIs
• Design patterns — understand when and why to use patterns such as Strategy, Factory, and Observer
• Data layer design — tables, schemas, relationships, indexes, queries, and data-store choices
• Design trade-offs — be ready to explain why you chose one approach over another
• Communication — practice talking through your design and defending your decisions
• Handling changing requirements — practice adapting your design when the interviewer introduces new requirements
• Mock LLD discussions — practice designing and explaining systems with an interviewer or peer

For Machine Coding

For Machine Coding, go deeper into implementation and execution.

Focus more on:

• Writing code quickly without compromising code quality
• Translating a well-defined problem statement into classes, interfaces, and APIs
• Implementing the complete flow end-to-end
• Handling edge cases and invalid inputs
• Writing meaningful unit tests
• Debugging and fixing issues quickly
• Refactoring code when needed
• Keeping the implementation extensible without over-engineering
• Managing time effectively during the round
• Practicing complete problems from start to finish within a fixed time limit