Design an Out-of-Order Event Processor

Problem

Design an event processor for an infinite, out-of-order event stream with validation and checksum handling (reported Box question).

Requirements

• Ingest events that may arrive out of order
• Validate each event and verify a checksum
• Emit events in order once contiguous
• Drop/flag corrupt events

What evaluators look for

• Clean separation: ingest, validate, buffer, emit
• Handling gaps and reordering with a buffer
• Idempotency and dedup

Extension

Bound the reorder buffer and handle a permanently missing sequence number.