This is the kind of question where you think you're done after sketching the classes and then they hit you with 'what about buses?' I hadn't pre-baked the consecutive-slot scan and it showed.
Start by clarifying requirements and scale, then design a class hierarchy for vehicles and parking slots with appropriate sizing rules. Focus on core operations (park, unpark, availability) and discuss data structures and concurrency for a multi-level lot.
Pro tip: Emphasize extensibility and real-world constraints like concurrency and pricing, showing you think beyond basic CRUD. Mention how your design would handle peak loads and dynamic pricing, which is crucial for Uber-scale systems.
Ask about number of levels, slots per level, vehicle types, and expected throughput. Clarify if slots can accommodate larger vehicles and if there are special slots (e.g., EV charging).
Identify main classes: ParkingLot, Level, ParkingSlot, Vehicle (with subclasses Motorcycle, Car, Bus). Define slot sizes (e.g., Small, Medium, Large) and mapping of vehicle types to compatible slot sizes.
Choose data structures to efficiently find available slots (e.g., per level, per size: min-heap or queue of free slots). For park, assign a suitable slot; for unpark, free the slot and update availability.
Discuss locking mechanisms (e.g., per level or per slot) to handle concurrent park/unpark. Consider distributed design if multiple instances, and how to maintain consistency.
Talk about trade-offs: simplicity vs. efficiency, memory vs. speed. Suggest extensions like reservation, dynamic pricing, and integration with payment systems.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
I started with a big if-else chain and the interviewer gave me a look.
Start by clarifying requirements and constraints, then propose a flexible design using an enum for vehicle types and slot types with a compatibility matrix or strategy pattern. Discuss trade-offs between simplicity and extensibility, and outline how to enforce compatibility at allocation time.
Pro tip: Mention that you would encapsulate compatibility logic in a single place (e.g., a method or class) to avoid scattering conditionals, and consider future vehicle types like bicycles or electric cars to show forward-thinking.
Ask about the types of vehicles and slots, expected scale, and whether compatibility rules might change or expand. Confirm that motorcycles can use both motorcycle and regular slots, while cars can only use regular slots.
Represent vehicle types and slot types as enums or classes. Create a compatibility mapping (e.g., a matrix or a method) that determines if a vehicle can park in a given slot.
When a vehicle arrives, filter available slots by compatibility. For motorcycles, prefer motorcycle slots first to conserve regular slots for cars, but allow fallback to regular slots if needed.
Encapsulate compatibility logic in a dedicated component (e.g., ParkingPolicy) to centralize rules. Use the strategy pattern or a simple map to allow easy addition of new vehicle or slot types.
Compare simple conditional checks versus a more extensible design. Consider performance, maintainability, and how to handle edge cases like full motorcycle slots but available regular slots.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
I assumed slot id at first and the interviewer asked me to clarify.
Start by clarifying the context: assume a parking system where a vehicle is parked at a location. Explain that unpark takes a unique identifier (e.g., vehicle ID or parking spot ID) and updates the state to mark the spot as available and the vehicle as unparked. Walk through the steps: validate the identifier, check current state, update state, and handle edge cases.
Pro tip: Mention idempotency and concurrency control (e.g., using a lock or version field) to prevent double-unparking, showing you think about real-world reliability.
Briefly state assumptions about the parking system, such as entities (Vehicle, ParkingSpot) and their states (parked, available).
Specify that unpark takes a unique identifier, such as vehicle ID or parking spot ID, and explain why that choice matters.
Detail the state updates: mark the parking spot as available, update the vehicle's status to unparked, and record timestamps if needed.
Walk through the steps: validate the identifier, check if currently parked, perform the state update, and handle errors (e.g., not found, already unparked).
Discuss concurrency, idempotency, and failure recovery to ensure the operation is robust.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Follow-up came at the end when I thought we were wrapping up.
Start by clarifying the billing requirements and constraints, then propose a modular pricing engine that decouples rate calculation from the core system. Walk through how you would integrate it with existing components, handle dynamic rates, and ensure scalability and correctness.
Pro tip: Emphasize idempotency and auditability in billing operations, as financial systems demand exactly-once processing and traceable calculations. Also, mention how you would handle rate changes and versioning to avoid retroactive billing errors.
Ask questions to understand billing granularity, rate structures (hourly, per slot type), and any constraints like real-time vs. batch processing.
Propose a flexible pricing service that encapsulates rate rules, supports multiple rate types, and can be updated without redeploying core services.
Explain how the pricing engine would interact with vehicle/slot management, user accounts, and payment processing, using events or APIs.
Discuss partitioning, caching, and idempotent billing operations to handle high volume and prevent double-charging.
Cover scenarios like rate changes, refunds, and disputes, and describe logging, metrics, and alerts for billing accuracy.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.