Medium data structure and algorithm practice puzzle.
Given a linked list, passed in as its values, and n, return the value n places from the end, or null if the list is shorter than n. Start a lead pointer n steps ahead, then move both pointers together until the lead runs off the end. The follower is now exactly n from the back. One pass, no length needed.
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 Replay Log, a pipeline you can run and download. See every Software Engineer project.
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