Easy data structure and algorithm practice puzzle.
Given an index i in a heap stored as an array, return its parent's index, or -1 for the root at index 0. The parent is (i - 1) / 2, rounded down, so both 1 and 2 have parent 0. A heap needs no pointers at all. The tree is just math on the index.
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 Track Window Auditor, a pipeline you can run and download. See every Software Engineer project.
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