Medium data structure and algorithm practice puzzle.
Given a linked list, passed in as its values, and a pivot, move every value below the pivot ahead of every value at or above it. Each side keeps its original order. Walk once, building two lists, "less" and "the rest", then join them.
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 Reading Replay Log, a pipeline you can run and download. See every Software Engineer project.
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