Easy data structure and algorithm practice puzzle.
Given a list of MIDI notes and a number of semitones, return every note lowered by that much. Subtract the same amount from each note and keep the order. Every note moves together, which is why the tune still sounds like itself, just lower.
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 Track Change Feed, a pipeline you can run and download. See every Software Engineer project.
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