Easy data structure and algorithm practice puzzle.
Given a linked list, passed in as its values from front to back, return its values in reverse order. Walk from the back to the front and collect each value. On a real linked list you can't walk backwards, so you'd flip each link with three pointers instead. Flip one before saving where it pointed and you've lost the rest of the list.
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 Login Undo Stack, a pipeline you can run and download. See every Software Engineer project.
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