Amazon·Software Engineer·Online Assessment (OA)·Intermediate

Intermediate

Jun 2026

Summary

Amazon SWE interview with a system design coding problem around a parking lot. Pretty straightforward on the surface but there's enough edge cases to trip you up if you're not careful about how you model the space allocation logic.

Questions Asked (1)

Design a parking lot system that handles vehicle entry and exit for three car sizes (small, medium, large), allocates the correct space type per vehicle, and reports available spaces after each operation.

System DesignAlgorithms & Data Structures

Author's notes

My first instinct was to just use three counters and call it done, which is basically the right call here.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then define core objects like Vehicle, ParkingSpot, and ParkingLot with appropriate data structures. Focus on allocation logic that matches vehicle size to spot size, and ensure efficient updates to available counts. Discuss trade-offs and potential extensions.

Pro tip: Demonstrate Amazon's leadership principles by proactively discussing scalability, concurrency, and customer obsession (e.g., minimizing wait times). Also, mention how you would handle edge cases like a large vehicle taking multiple small spots.

1. Clarify Requirements

Ask questions to understand scope: number of spots per size, entry/exit rates, concurrency needs, and whether spots can be combined. Confirm expected operations and reporting.

2. Design Data Model

Define classes: Vehicle (size), ParkingSpot (size, availability), ParkingLot (spots, available counts). Choose data structures like lists or priority queues for efficient allocation.

3. Implement Allocation Logic

For entry, find a spot matching vehicle size; if none, consider larger spots or combinations. For exit, free the spot and update counts. Ensure thread safety if needed.

4. Handle Reporting and Edge Cases

Maintain real-time counts of available spots per size. Discuss handling of full capacity, invalid operations, and potential optimizations like reserving spots.

5. Discuss Scalability and Trade-offs

Talk about scaling to multiple lots, distributed systems, and trade-offs between simplicity and efficiency. Mention possible extensions like dynamic pricing or EV charging.

Key Points to Mention

Object-oriented design with clear separation of concerns (Vehicle, Spot, Lot).
Efficient data structures for allocation (e.g., hash maps for counts, queues for spots).
Concurrency handling for simultaneous entry/exit (locks, atomic operations).
Strategy for allocating larger spots to smaller vehicles (e.g., best-fit).
Real-time availability reporting and consistency.
Scalability considerations: multiple lots, distributed coordination, and load balancing.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.