Easy data structure and algorithm practice puzzle.
Given an opponent's rating deviation, which is how unsure the ladder is about its rating, return how much its result should count, rounded to four decimal places. A deviation of 0 means fully trusted, so the weight is 1. The less sure the ladder is, the smaller the weight. Beating a puzzle nobody has tried yet shouldn't move your rating as much as beating one the ladder knows well.
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 Match Forecaster, a pipeline you can run and download. See every Software Engineer project.
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