Medium data structure and algorithm practice puzzle.
Given an array of customer spending, return how many customers spent more than the average. This takes TWO passes. The first one adds everything up to find the average. The second one counts who's above it. You can't do it in one, because you don't know the average until you've seen every value.
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 Range Service, a pipeline you can run and download. See every Software Engineer project.
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