Machine Coding Round Preparation
What is a Machine Coding Round?
A machine coding round is a hands-on coding interview (typically 60–90 minutes) where you design and implement a working system from scratch. Unlike DSA rounds that test algorithmic thinking, machine coding evaluates your ability to build real software — clean code, good design, and working functionality.
Companies like Flipkart, Uber, Walmart, PhonePe, CRED, Ola, Meesho, and many startups use this round extensively.
What Interviewers Evaluate
1. Requirements Gathering (10–15%)
- Do you ask clarifying questions before coding?
- Do you identify edge cases upfront?
- Do you define scope and prioritize features?
2. Class Design & Architecture (25–30%)
- Are your classes cohesive with clear responsibilities?
- Do you use appropriate design patterns?
- Is your design extensible and maintainable?
- Do you follow SOLID principles?
3. Code Quality (20–25%)
- Clean, readable, well-structured code
- Proper naming conventions
- Error handling and input validation
- No code duplication (DRY principle)
4. Working Solution (25–30%)
- Does the code compile and run?
- Do core features work correctly?
- Can you demo the solution?
- Are edge cases handled?
5. Communication & Problem-Solving (10–15%)
- Do you explain your thought process?
- How do you handle feedback and pivots?
- Do you manage time effectively?
Common Machine Coding Problems
| Problem | Key Concepts | Difficulty |
|---|---|---|
| Parking Lot | OOP, Strategy Pattern, Enums | Medium |
| Elevator System | State Machine, Scheduling | Medium-Hard |
| Library Management | CRUD, Relationships, Fines | Medium |
| Splitwise | Graph Algorithms, Settlement | Medium |
| Rate Limiter | Algorithms, Concurrency | Medium-Hard |
| LRU Cache | Data Structures, O(1) ops | Medium |
| Task Scheduler | Priority Queues, Dependencies | Medium-Hard |
| URL Shortener | Hashing, Database Design | Easy-Medium |
| Chess/Board Game | State Machine, Rules Engine | Hard |
| Cab Booking | Matching, Geo-spatial | Hard |
Time Management Strategy
Total Time: 75 minutes (typical)
[0-5 min] → Read requirements, ask questions
[5-15 min] → Identify entities, relationships, design classes
[15-20 min] → Discuss approach with interviewer
[20-55 min] → Implement core functionality
[55-65 min] → Test, fix bugs, handle edge cases
[65-75 min] → Refactor, discuss improvements
General Approach
- Start with requirements — list functional and non-functional requirements
- Identify entities — what are the core objects?
- Define relationships — how do entities interact?
- Choose design patterns — which patterns fit naturally?
- Implement incrementally — core features first, then enhancements
- Test as you go — don’t wait until the end
Files in This Section
- approach.md — Detailed approach methodology
- design-principles.md — SOLID and design patterns
- parking-lot.md — Parking lot system
- elevator.md — Elevator system
- library-management.md — Library management
- splitwise.md — Expense splitting
- rate-limiter.md — Rate limiter
- cache-lru.md — LRU cache
- task-scheduler.md — Task scheduler
Tips for Success
- Practice on paper first — sketch class diagrams before coding
- Use your IDE well — know shortcuts, auto-complete, debugging
- Start simple — get a working skeleton, then add features
- Don’t over-engineer — interviewer wants working code, not a perfect framework
- Talk through decisions — explain WHY you chose a pattern or structure
- Handle errors gracefully — null checks, invalid inputs, edge cases
- Write testable code — even if you don’t write tests, make it testable