Medium data structure and algorithm practice puzzle.
Given an array, return a new array where each spot holds the product of every other number, without using division. Each answer is everything to its left times everything to its right. So make one pass from the left building running products, and one pass from the right doing the same, then multiply them together. Two passes, O(n).
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 Packet Billing Run, a pipeline you can run and download. See every Software Engineer project.
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