Hard data structure and algorithm practice puzzle.
Given two ranked lists of documents, return every document sorted by its fused score, best first. A document at position i (starting from 0) in a list earns 1 / (61 + i). Add up what it earns from both lists. Ties keep the order they first appeared in, list A first. It only looks at rank, so the two search engines' raw scores never need to agree.
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 Request Billing Run, a pipeline you can run and download. See every Software Engineer project.
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