Medium data structure and algorithm practice puzzle.
Given an array and a limit, return how many pairs add up to less than the limit. Sort it first. Put one pointer at each end. If the two ends add up to less than the limit, then the left value pairs with everything up to the right pointer, so count all of those at once and move left forward. Otherwise, move right back.
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 Clause Burst Detector, a pipeline you can run and download. See every Software Engineer project.
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