Medium data structure and algorithm practice puzzle.
Given a list where deps[i] is the services that service i needs, and one service that just failed, return how many services end up down, counting the one that failed. A service goes down if anything it depends on is down, so the failure spreads backward along the dependency arrows. Keep marking services down until nothing changes.
Solve it three ways: snap the jigsaw pieces together, fill in the blanks, or type it from scratch against the tests. This one is free.
Every line of the solution comes with a note explaining why it is there, and a step by step replay shows the code running. At level 3, where you type it yourself, you can ask for an AI mock interview on this problem that ends with a hiring manager's scorecard.
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