Uber

How this question breaks down

1. 1LocationsCore28 minTake a position fix from every online driver every four seconds, keep only the newest one in a memory index that answers "who is near here?" in milliseconds, and hand the full stream to everything else that needs it.
2. 2MatchingCore22 minCollect ride requests for a couple of seconds, pair them with free drivers to cut everyone's pickup time rather than just the first rider's, and offer each ride to one driver at a time without ever promising a driver to two riders.
3. 3TripsCore33 minModel each trip as a state machine with one writer and one strongly consistent store, make every transition a conditional, idempotent write that commits with its event, and let timers and events drive what follows.
4. 4PricingCore25 minCount demand and free drivers per hexagon every minute from streams that already exist, turn the ratio into a smoothed, capped multiplier, and lock it into a short-lived quote so the price a rider accepts is the price they pay.

Work through the parts in order and you’ve covered the full design. Each part is one topic.