A Step-by-Step Guide
If you’re aiming to crack interviews at product-based companies like Flipkart, Swiggy, Uber, or startups, you’ll often
face a machine coding round. This round goes beyond traditional algorithmic questions and tests your ability to
build scalable, modular, and working software systems in real time.
This article provides a complete guide to understanding the machine coding round, including a sample question
(Rate Limiter) and step-by-step strategy to tackle such problems effectively.
What Is a Machine Coding Round?
A machine coding round is a time-bound coding interview where you’re asked to design and implement a small system or application. Unlike typical data structure or algorithm questions, this round assesses:
Object-oriented design skills
Clean code structure
Modularity and separation of concerns
Ability to handle edge cases and real-world constraints
Writing basic test cases to validate functionality
The round usually lasts between 1.5 to 3 hours and is considered a crucial stage for backend, full-stack, and system design-focused roles.
Sample Question: Design a Rate Limiter
To help you understand the process, let’s take a classic machine coding round question:
Problem Statement:
Design a Rate Limiter that restricts users to a maximum of N API requests per minute.
Requirements:
1 Each user can make up to N requests per minute.
2 Further requests within the same time window should be denied.
3 Implement a function like allowRequest(userId) which:
Returns true if the request is allowed
Returns false if the rate limit is exceeded
This is a simplified yet realistic system design problem that tests your ability to work with time-based constraints,
state management, and user-specific logic.
Step-by-Step Approach to Solving a Machine Coding Round
Problem
Step 1: Clarify Requirements
Before diving into code or even design, ask clarifying questions. In machine coding rounds, requirements are often deliberately vague to see how well you handle ambiguity.
Ask questions like:
Is the time window fixed or sliding?
Is the system single-threaded or does it need concurrency control?
Should the data be stored in-memory or persisted?
What’s the expected number of users or requests?
For the Rate Limiter example, we assume:
A fixed 60-second window
An in-memory solution
No concurrency or persistence required
Step 2: Design the Data Structures
Think carefully about how to store and manage state.
For a rate limiter:
You need to track how many requests a user has made in the last 60 seconds.
A good choice is to maintain a map of user IDs to timestamps of requests.
When a new request comes in, you’ll:
Remove timestamps older than 60 seconds
Check if the remaining timestamps are less than the allowed limit
Decide whether to allow or deny the request
Keep it simple, but scalable and extensible.
Step 3: Identify the Core Components
Structure your solution into modular components. For example:
1 RateLimiter class:
Responsible for handling rate-limiting logic per user
1 RequestTracker or UserRequestLog:
Keeps track of timestamps per user
1 RequestManager (optional):
Coordinates between multiple users and their limits
1 Clock abstraction (optional):
Useful for testing and decoupling system time
These abstractions help in writing clean, testable, and extensible code—key factors in a successful machine coding
round.
Step 4: Write a Clean, Object-Oriented Design
Use OOP principles to organize your code:
Encapsulate logic inside methods
Avoid repetition by reusing helper functions
Use meaningful class and method names
Make it extensible (e.g., to support per-user rate limits)
Even without writing the code, plan your classes and methods using comments or pseudocode before
implementation.
Step 5: Handle Edge Cases
Think through all possible edge scenarios:
What if the user is new and has no request history?
What if all previous requests are expired?
What if system time changes or is out of sync?
During machine coding rounds, interviewers often test how well you anticipate and handle edge cases. Discuss
these proactively even if not all are implemented.
Step 6: Write Basic Test Cases
After implementing your logic, write some basic test cases to validate:
First-time user making a request
Multiple requests within the allowed limit
A request that exceeds the limit
A request after the time window has passed
Automated test cases aren’t always expected, but even showing a main method or simple input/outputA
demonstration adds great value and shows you’re thorough.
Step 7: Explain Your Thought Process
Don’t stay silent during the round. Communicate:
Why you chose a certain data structure
How your design handles scalability
What can be improved in a production version (e.g., using Redis, adding concurrency, etc.)
A machine coding round is not just about code—it’s about how you think, design, and communicate.
Best Practices for Machine Coding Rounds
1. Follow SOLID Principles
Use OOP best practices. Keep your classes small and focused. For example:
Single Responsibility: One class for tracking requests, another for applying the rate limit
Open/Closed: Easy to extend limits to hourly or daily without changing core logic
2. Optimize for Readability
Use descriptive names and add comments where logic is tricky. Clean code shows maturity.
3. Don’t Over-Engineer
Stick to the problem. Don’t build APIs, UIs, or databases unless required. Simpler is better.
4. Think About Scalability
Be ready to discuss:
How this would work for millions of users
Trade-offs between in-memory vs persistent storage
How to implement a distributed version of your solution
5. Time Management
Spend:
10–15 minutes planning
60–80 minutes coding
Last 10–15 minutes testing and refactoring
Leave some buffer to fix bugs or improve structure.
Common Follow-up Questions After the Round
How would you handle concurrency?
Can this design be distributed across multiple servers?
How would you implement different limits for different users?
What would change if the window were sliding instead of fixed?
Prepare to answer these confidently—they’re great opportunities to showcase deeper system design knowledge.
Conclusion
The machine coding round is one of the most important stages in modern tech interviews. It tests your ability to build real-world software—clean, scalable, and robust. Unlike algorithm rounds, it focuses on practical skills that developers use every day.
By breaking the problem down into manageable steps—requirement gathering, design, modular implementation, and testing—you can systematically tackle even the most complex problems.
Whether it’s a rate limiter, parking lot system, or food ordering platform, the key is to think like a software
engineer, not just a coder. With enough practice and a structured approach, you’ll be well-equipped to ace your next machine coding round.
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