Medium data structure and algorithm practice puzzle.
Given a directed graph as an adjacency list, a start, and a target, return true if there's any path from start to target. Use depth-first search with a stack and a set of visited nodes. The visited set is what stops you from going around a loop forever. You only need to know IF there's a path, not the shortest one.
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.
Then grow it into a real project with the Software Engineer button: this puzzle becomes the Step Dependency Resolver, a pipeline you can run and download. See every Software Engineer project.
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