Hard data structure and algorithm practice puzzle.
Given a sorted linked list, passed in as its values, remove EVERY value that appears more than once, keeping only the values that showed up exactly once. So [1, 1, 1, 2, 3] becomes [2, 3]. Count each value first, then keep the ones with a count of 1. Repeated values disappear completely instead of being cut down to one.
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 Read Stream Buffer, a pipeline you can run and download. See every Software Engineer project.
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