Seemed deceptively simple at first and I think I wasted the first few minutes going too shallow.
Start by clarifying the scope and requirements of the vending machine, such as the types of items, payment methods, and expected scale. Then, design a high-level architecture covering the main components and their interactions, and dive into key subsystems like inventory management, payment processing, and state transitions. Discuss trade-offs and potential bottlenecks, and consider how the design would scale or handle edge cases.
Pro tip: Demonstrate maturity by proactively discussing failure modes and recovery strategies, such as handling power outages or network failures, and how to ensure data consistency. This shows you think beyond the happy path and consider real-world reliability.
Ask questions to understand the scope: What items are sold? What payment methods? Is it networked? What scale (single machine vs. fleet)? What are the key features (e.g., refunds, inventory tracking)?
Outline the main components: user interface, payment system, inventory system, dispensing mechanism, and backend (if networked). Describe how they interact and the overall flow of a transaction.
Choose 1-2 critical areas to detail, such as the state machine for a transaction, inventory management with concurrency control, or payment processing with idempotency. Discuss data models and APIs.
Discuss design decisions and trade-offs (e.g., consistency vs. availability, synchronous vs. asynchronous payment). Cover edge cases like item out of stock, payment failure, and power loss.
Explain how the design can scale to multiple machines, support new payment methods, or integrate with remote monitoring. Mention potential bottlenecks and how to mitigate them.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.