Full Stack Developer signal: hash map + dedupe in a subscription billing context. This is a ProdMatch-owned full stack engineer drill, framed as a May 2026 Uber Revenue Platform simulation, not a copied platform question.
Company context
Uber · Revenue Platform
Freshness
May 2026
Product surface
subscription billing
ProdMatch interview simulation based on product-team patterns; not a claim of a real company question.
For subscription billing, collapse duplicate invoices by external ID. Keep the newest event per ID and return IDs in first-seen order.
Input
Output
Constraints
Concepts
[(a,1),(b,1),(a,3)] -> [(a,3),(b,1)]
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