Real-time location sharing
Design a real-time location-sharing feature (friends/family see each other's live location on a map) for 100M users in groups/circles, where a viewer should see a member's marker move within a few seconds of the member moving. Cover how updates fan out to viewers, how you handle the social graph, and privacy/permission controls.
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.