Hot stories ranking
Design a 'top stories' / hot-ranking system for a community link-aggregator (like a tech-news front page). Stories are ranked by a score combining votes, comments, and age (newer rises, then decays). Scale: 5M users, 50k new stories/day, the front page is read millions of times/hour, and a story's rank must update within ~1 minute of new votes.
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.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 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.