Library checkout and holds
Design a library checkout system. The library owns multiple physical copies of each book title. A member can borrow an available copy, with a due date set on checkout; returning a copy makes it available again, and overdue items accrue a small fine. Members can also place a hold on a title that has no copies available. Cover the data model, how a checkout works, and how holds are handled.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify4:00 left
Estimate4:00 planned
Design11:30 planned
Deep dive9:30 planned
Failure6:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.