Graphshard70 minSoftware Engineer

Notifications Dependency DAG Recovery

Name: ProdMatch.ai
Availability: InStock

Software Engineer signal: topological sort + cycle detection in a notification delivery context. This is a ProdMatch-owned software engineer drill, framed as a March 2026 Unacademy Messaging Platform simulation, not a copied platform question.

Company context

Unacademy · Messaging Platform

Freshness

March 2026

Product surface

notification delivery

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

Question

You own notification delivery for a Software Engineer loop. Given messages and directed dependencies between them, return a valid execution order. If a cycle exists, return an empty list and identify that the rollout is blocked.

Input

n nodes labelled 0..n-1 and dependency pairs [before, after].

Output

A valid order of all nodes, or [] when dependencies contain a cycle.

Constraints

1 <= n <= 200000
0 <= dependencies.length <= 400000
The graph may be disconnected.

Concepts

invariants
API correctness
graph modelling
topological sort
cycle detection
dependency graph

messages: 4, deps: [[0,1],[0,2],[2,3]] -> [0,1,2,3] or [0,2,1,3]

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

Mark visited when enqueueing, not after repeated dequeue.
Do not ignore disconnected components if the product surface can have them.

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