Medium data structure and algorithm practice puzzle.
Given a list of numbers, return the length of the longest zigzag you can pick out of it, where the steps go up, down, up, down (or the other way). Keep two counts: the longest zigzag ending with a step up, and the longest ending with a step down. A rise extends the down count by 1, and a fall extends the up count. Equal neighbors are neither, so they change nothing.
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 Login Priority Desk, a pipeline you can run and download. See every Software Engineer project.
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