Hard data structure and algorithm practice puzzle.
Given a root note, return the seven notes of its major scale. Start at the root and step up by 2, 2, 1, 2, 2, 2 semitones, adding each new note as you go. So a root of 0 gives [0, 2, 4, 5, 7, 9, 11]. Walking a list of steps from a starting point is a pattern you'll use far beyond music.
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 Intake Pipeline, a pipeline you can run and download. See every Software Engineer project.
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