Graphsmedium45 minData Engineer

Watermark Dependency DAG Recovery

Data Engineer signal: topological sort + cycle detection in a stream watermarking context. This is a ProdMatch-owned data engineer drill, framed as a March 2026 Apple Realtime Data simulation, not a copied platform question.

Company context

Apple · Realtime Data

Freshness

March 2026

Product surface

stream watermarking

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

Question

You own stream watermarking for a Data Engineer loop. Given events 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

stream windows
watermarks
lineage DAGs
topological sort
cycle detection
dependency graph

events: 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.

Next Similar Problems

Watermark Evidence Path Finderhard Lineage Dependency DAG Recoveryhard Lineage Evidence Path Findermedium