Hard data structure and algorithm practice puzzle.
Given a linked list, passed in as its values, and two positions left and right (starting from 0), reverse just the part from left to right and leave the rest alone. So [1, 2, 3, 4, 5] from 1 to 3 is [1, 4, 3, 2, 5]. On a real linked list, the reversing is easy. The tricky part is reconnecting both ends.
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 Ticket Replay Log, a pipeline you can run and download. See every Software Engineer project.
Browse all 576 puzzles