Heap / Priority Queuehard70 minBackend Engineer

Ledger Real-Time Top-K Prioritizer

Backend Engineer signal: heap + top-k in a wallet ledger context. This is a ProdMatch-owned backend engineer drill, framed as a April 2026 ServiceNow Fintech Ledger simulation, not a copied platform question.

Company context

ServiceNow · Fintech Ledger

Freshness

April 2026

Product surface

wallet ledger

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

Question

Your Fintech Ledger team needs a live top-k view for transactions. 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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