Hard data structure and algorithm practice puzzle.
Given a matrix, return its values in spiral order: across the top, down the right side, back along the bottom, up the left side, then inward. Keep four boundaries, top, bottom, left, and right, and pull each one in after you walk its edge. Before walking the bottom and left edges, check that the boundaries haven't crossed, or a single leftover row or column gets read twice.
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 Order Cluster Finder, a pipeline you can run and download. See every Software Engineer project.
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