Heap / Priority Queuehard70 minFull Stack Developer

Realtime Real-Time Top-K Prioritizer

Full Stack Developer signal: heap + top-k in a realtime collaboration context. This is a ProdMatch-owned full stack engineer drill, framed as a May 2026 Stripe Realtime Platform simulation, not a copied platform question.

Company context

Stripe · Realtime Platform

Freshness

May 2026

Product surface

realtime collaboration

ProdMatch interview simulation based on product-team patterns; not a claim of a real company question.

Question

Your Realtime Platform team needs a live top-k view for patches. Each update changes an item's score. Return the current top k item IDs after each update, ordered by score desc then ID asc.

Input

Initial scores, k, and update stream [id, delta].

Output

Top-k IDs after every update.

Constraints

1 <= items <= 200000
1 <= updates <= 200000
Scores can be negative.

Concepts

workflow graphs
API pagination
cache invalidation
heap
top-k
streaming rank

scores: [5,1,3], k=2, update [1,+5] -> [1,0]

Approach

Try framing your own approach first. The 30 seconds you think before peeking is where learning happens.

Clean Solution

Reveal the approach first.

How well did you understand?

Your rating tunes when this problem shows up again.

Common Mistakes

Use a stable tie-breaker for equal scores.
Do not sort the full stream when k is small.

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