Easy data structure and algorithm practice puzzle.
Given [hours, rate, retainer], return how much the client still owes. The fee is hours times rate. Subtract the retainer they already paid. If that's below 0, return 0, because a credit isn't a negative bill. Limiting a value like that is called clamping, and it's one of the easiest steps to forget.
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 Clause Integrity Check, a pipeline you can run and download. See every Software Engineer project.
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