Ads bidding and ranking
Design the ML system behind an ads-targeting and real-time-bidding service that, for each ad opportunity, selects and ranks candidate ads and computes a bid within a 50ms p99 budget at 100k requests/sec. It must predict click and conversion probability, respect per-advertiser budgets and pacing, and run a second-price-style auction. Cover candidate selection, the prediction models, how bids and budgets are managed, and the calibration requirement.
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.
Clarify6:00 left
Estimate6:00 planned
Design18:30 planned
Deep dive14:30 planned
Failure10:00 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.