Location-based AR proximity
Design the proximity/presence backend for a location-based AR game (think Pokémon-GO-style) where 10M concurrent players see nearby players, spawned objects, and events within ~500m, refreshed continuously as they walk around. Movement is constant and the world is densely populated in cities. Cover the spatial index, how a client subscribes to its surroundings, and how you bound update volume.
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.
Clarify4:00 left
Estimate4:00 planned
Design11:30 planned
Deep dive9:30 planned
Failure6:00 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.