Per-entity final state from an at-least-once, reordered stream.
Name it
Say what this problem really is, professionally — the concept + when it bites. practice the framing →
Explain it out loud
Say it in your own words — but hit these: dedup on eventid · sort by timestamp · final state · at-least-once · reject
checking microphone…
Code it (7-step rhythm, narrate)
Clarify → approach → data model → narrate → edge → test → tradeoff. AI off. Problem: event processor →
Edge cases — say + handle each
Say the trade-off
“You give up simple in-arrival-order processing for correctness under duplication and reordering.”
checking microphone…
Answer the follow-up
Why dedup on the eventId and not the whole event object?
Catch the classic bug
Spot the wrong implementation in <60s. open the bug drill →