Heap / Priority Queuemedium45 minBackend Engineer

RateLimit Real-Time Top-K Prioritizer

Backend Engineer signal: heap + top-k in a tenant rate limits context. This is a ProdMatch-owned backend engineer drill, framed as a April 2026 Ola API Gateway simulation, not a copied platform question.

Company context

Ola · API Gateway

Freshness

April 2026

Product surface

tenant rate limits

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

Question

Your API Gateway team needs a live top-k view for calls. 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

idempotency
queues
rate limiting
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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