Hard data structure and algorithm practice puzzle.
Given x and y, return their Morton code by interleaving their bits: x's bits go in the even positions and y's bits go in the odd ones. So x = 1, y = 0 gives 1, and x = 0, y = 1 gives 2. Sorting by this code walks through space in a Z pattern, which keeps nearby points close together in the list.
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 Flag Store, a pipeline you can run and download. See every Software Engineer project.
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