Medium data structure and algorithm practice puzzle.
Given predictions and true labels, both 0 or 1, return the recall, rounded to 3 decimals. Of everything that really was 1, what fraction did the model catch? Count true positives and false negatives, and divide true positives by their total. If there were no real 1s, return 0. Flag everything and recall hits 1, but precision falls apart.
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 Sample Stats Roll-up, a pipeline you can run and download. See every Software Engineer project.
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