Personalized send-time optimization
Design a personalized notification/email send-time + content-selection system for a 50M-user app that decides for each user WHICH message to send and WHEN, to maximize long-term engagement without fatiguing users into unsubscribing. It must learn per-user from sparse feedback (opens/unsubs), adapt within days, and cap message frequency.
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.