Hard data structure and algorithm practice puzzle.
Given two arrays that line up, monthly revenue and monthly cost, return the biggest profit from any single month. Work out each month's profit (revenue minus cost) first, then take the biggest. The best month isn't always the one with the most revenue.
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 Trade Billing Run, a pipeline you can run and download. See every Software Engineer project.
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