Design a parking lot system
Company: BlackRock
Role: Software Engineer
Category: System Design
Difficulty: easy
Interview Round: Technical Screen
Design a parking lot system (software + core components) that supports multiple entry/exit gates, different spot types, ticketing, and payment.
## Functional requirements
- Vehicles enter via an entry gate and receive a ticket.
- Vehicles park in an appropriate available spot (e.g., compact/large/EV/handicap).
- Vehicles exit via an exit gate and pay based on time parked (and possibly vehicle/spot type).
- The system should:
- Track spot occupancy and availability in near real-time.
- Handle multiple floors/zones.
- Support lost-ticket scenarios and payment failures.
## Non-functional requirements
- Correctness under concurrent arrivals/departures.
- High availability for gate operations (tickets and exits should still work during partial outages).
- Low latency at gates (avoid long lines).
- Auditable records for payments and occupancy.
Provide:
- High-level architecture
- Core data model
- Key APIs
- Main flows (enter, park, exit, payment)
- Concurrency/consistency approach and failure handling
Quick Answer: This question evaluates system design competencies such as scalable distributed architecture, real-time state management, data modeling, API design, concurrency control, fault tolerance, payment/audit logging, and operational concerns like latency and availability.