Real-time driver-rider matching
Design the real-time driver-rider matching engine for a ride-hailing service in a dense metro: ~500k drivers streaming GPS pings every 4 seconds, riders requesting in bursts, and a hard requirement that a match decision return in under 1 second using positions no older than ~5 seconds. Describe how you index moving drivers, how a rider request finds nearby candidates fast, how you avoid double-matching one driver to two riders, and what you do when supply is far below demand in a surge cell.
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.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 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.