Medium data structure and algorithm practice puzzle.
Given a list of builds where false is good and true is broken, and once a build breaks every later one is broken too, return the index of the first broken one, or -1. Binary search: if mid is broken, the first bad one is at mid or before it. If not, it's after. This is exactly how git bisect finds the commit that broke things.
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 Frame Ordered Index, a pipeline you can run and download. See every Software Engineer project.
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