Medium data structure and algorithm practice puzzle.
Given disk requests by cylinder, where the head is now, and the highest cylinder, return how far the head travels. The head moves up first, serving every request at or above it in order, and keeps going to the highest cylinder. Then, if anything is left below, it reverses and serves those on the way down. If nothing is left below, it stops at the last request. It works just like an elevator.
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 Trip Change Feed, a pipeline you can run and download. See every Software Engineer project.
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