Graphshard70 minDevOps / SRE Engineer

Logs Dependency DAG Recovery

DevOps / SRE Engineer signal: topological sort + cycle detection in a log compaction context. This is a ProdMatch-owned devops sre drill, framed as a March 2026 Unacademy Observability simulation, not a copied platform question.

Company context

Unacademy · Observability

Freshness

March 2026

Product surface

log compaction

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

Question

You own log compaction for a DevOps / SRE Engineer loop. Given spans 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

blast-radius graphs
alert dedupe
rolling windows
topological sort
cycle detection
dependency graph

spans: 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.

Next Similar Problems

Incident Dependency DAG Recoverymedium Incident Evidence Path Finderhard Deploy Dependency DAG Recoveryhard