Medium data structure and algorithm practice puzzle.
Given a binary tree, return how many levels deep it goes. An empty tree is 0. Otherwise, it's 1 for this node plus the deeper of its two subtrees. Depth matters because it bounds everything else you do to a tree: a balanced one finds a key in O(log n), and one that's collapsed into a chain takes O(n).
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 Order Hierarchy Report, a pipeline you can run and download. See every Software Engineer project.
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