Graphshard70 minBackend Engineer

Routing Dependency DAG Recovery

Backend Engineer signal: topological sort + cycle detection in a service routing context. This is a ProdMatch-owned backend engineer drill, framed as a May 2026 Google Core Infra simulation, not a copied platform question.

Company context

Google · Core Infra

Freshness

May 2026

Product surface

service routing

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

Question

You own service routing for a Backend Engineer loop. Given services 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

idempotency
queues
rate limiting
topological sort
cycle detection
dependency graph

services: 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?

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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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