Machine Coding Round vs LLD Round: What Is the Difference?
A machine coding round asks you to build a small working program in 90 to 120 minutes. It is graded on the code that runs at the end. A low-level design (LLD) round asks you to design the classes and interfaces for a problem in 45 to 60 minutes. It is graded on the design discussion, usually with no running code at all. The two rounds often use the same problem, such as a parking lot or a snake and ladder game. The difference is in what you hand over and how it is judged.
Quick comparison
| Machine coding round | LLD round | |
|---|---|---|
| Duration | 90 to 120 minutes, sometimes longer | 45 to 60 minutes |
| Deliverable | A program that compiles and runs, with tests | A class diagram and method signatures, spoken or drawn |
| What is graded | Working output, code structure, edge cases | Class boundaries, patterns, extensibility, the discussion |
| Tools allowed | Your own laptop and editor, usually offline | Whiteboard, shared document, or a drawing tool |
| Typical problems | Parking lot, snake and ladder, Splitwise, a small booking or inventory system | Parking lot, elevator, LRU cache, notification service |
| Where it is used | Widely reported at India-based product companies such as Flipkart, Uber India, Swiggy, PhonePe, and Navi | Standard at most product companies worldwide |
What a machine coding grader looks for
The first check is whether the program runs. A program that handles the main flow with one feature missing scores higher than one that models everything and crashes. The second check is whether the model is clean. That means classes named after the nouns in the problem, one responsibility each, and no business logic in the main method. The third is extensibility: a new vehicle type or discount rule is added by adding a class, not by editing several. The fourth is edge cases. A full parking lot, a player landing past the last square, and an expense that does not divide evenly are the usual ones.
Graders usually read the code after the session, sometimes without you present. Structure and naming therefore matter more than they do in a live interview. A short README that says how to run the program and which features were left out is expected. What is machine coding round in Uber? describes one company's version in detail.
What an LLD grader looks for
An LLD grader is listening rather than reading. The first check is whether you clarified requirements before drawing anything. The design for one server and the design for a cluster are different, and the grader wants to see you ask which one is wanted. The second is the class diagram: the right entities, the right relationship between each pair, and an interface wherever behavior varies. The third is correct use of two or three design patterns. Name each one as you apply it, and do not force one where a plain method would do. The fourth is the one concurrency case, such as two users booking the same seat. You are expected to find it and say how the race is prevented. The full list of problems and the skill each tests is in Low-Level Design Interview Questions.
How both differ from the system design round
A high-level design (HLD) round is the one most people mean by "system design interview". It asks how a whole product, such as a chat service, is built from services, databases, caches, and queues. It is graded on scale and trade-offs rather than on classes. Machine coding and LLD both concern the inside of one service. Neither discusses servers, sharding, or traffic. Which rounds you get depends on level. Machine coding and LLD are common for engineers with zero to five years of experience, and the HLD round is added for senior roles. If your question was the difference between the low-level and high-level design rounds, that is answered in LLD vs. HLD.
Practice for each round
For machine coding, build a complete program with tests in 90 minutes, once a week. Use a problem statement you have not seen before. Have a runnable skeleton in the first 10 minutes, then add features in the order the statement lists them. Stop adding at 75 minutes and write the tests and the README. Prepare a project template in your language beforehand, so the build, the test runner, and the folder layout cost no time on the day.
For LLD, practice class diagrams out loud. Take one problem and draw the diagram on paper while explaining each class and relationship to a listener or a recording. Then write the two most important method signatures. Time it at 30 minutes and repeat with a new problem the next day. Speaking while drawing is a separate skill from either one alone. What to Expect in a Low-Level Design Interview Round describes how the hour is run.
How to Prepare
- Practice the shared problem set. The same fifteen or so problems appear in both rounds. Solving each one as a diagram and then as a program prepares you twice.
- Study the patterns by problem. Grokking the Object-Oriented Design Interview works through the parking lot, library, hotel, and movie booking designs with class diagrams.
- Cover the concurrency case. Grokking Multithreading and Concurrency for Coding Interviews covers the locking that both rounds ask about.
- Do a timed mock. A mock interview with an engineer who grades the way the company does shows which of the four checks you miss.
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