Hard data structure and algorithm practice puzzle.
Given kids' ratings in a row, give each kid at least one candy, and give any kid rated higher than a neighbor more candy than that neighbor. Return the fewest total candies. Make two passes. Left to right, a kid rated higher than the one before gets one more than them. Right to left, do the same against the kid after, keeping whichever count is bigger.
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 Document Slot Packer, a pipeline you can run and download. See every Software Engineer project.
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