Low-Level Design / Machine Coding
📚 New to machine coding? Start with the LLD Fundamentals — covers SOLID, design patterns, concurrency, and the 90-minute approach.
Machine-coding problems asked at PhonePe, Flipkart, Swiggy, Razorpay, and other Indian tech companies. Each solution uses OOP, design patterns (Strategy, State, Observer), and is runnable end-to-end with a demo class.
Problems
| # | Problem | Key Patterns | Companies | Languages |
|---|---|---|---|---|
| 1 | 🅿️ Parking Lot | Strategy, Polymorphism, Factory | Flipkart, PhonePe, Amazon | Java |
| 2 | 🗃️ Multilevel Cache (coming soon) | Strategy (LRU/LFU), Composition, Facade | PhonePe, Flipkart | Java, Python |
| 3 | 📨 Message Broker (coming soon) | Facade, Composition, Concurrency | PhonePe, Uber | Java, Python |
| 4 | 🎫 Customer Issue Resolution (coming soon) | Strategy, State Machine, Facade | PhonePe | Java, Python |
| 5 | 🐍 Snake & Ladder (coming soon) | Strategy, State, Command | PhonePe, Flipkart | Java, Python, C++ |
| 6 | 💸 Splitwise (coming soon) | Strategy (split types), Aggregation | PhonePe, Flipkart | Java, Python, C++ |
| 7 | 🍽️ Restaurant Booking (coming soon) | Reservation conflicts, Concurrency | PhonePe | Java |
| 8 | 📱 App Version Manager (coming soon) | Strategy (rollout), Adapter, Factory | PhonePe | Java |
What interviewers grade on
- Working demo class — must compile and run end-to-end.
- Separation of concerns — multiple files/classes, each doing one thing.
- Strategy pattern somewhere — pricing, eviction, assignment, scoring.
- Extensibility — adding a new variant = one new class, no edits to existing.
- Edge cases — null inputs, capacity limits, state machine violations.
- Thread-safety — when shared mutable state exists.
More problems coming weekly. Drop a request in the comments below 👇
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