Cart recommendations
Design a 'frequently bought together' and real-time cart/session recommendation system for a grocery-delivery app. Suggestions must update as items are added to the cart ('you added pasta — add sauce?'), reflect within-session intent, handle 100M products with massive popularity skew, and serve under 100ms as the cart changes.
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.
Clarify5:30 left
Estimate5:30 planned
Design16:30 planned
Deep dive13:30 planned
Failure9:00 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.