Code Room
System designMedium
Question
Design a shopping cart service that persists carts for logged-in users and guests, and merges a guest cart into the user's cart on login.
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.
Learn the concepts
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Run or narrate your approach, then ask the coach.