Hard data structure and algorithm practice puzzle.
Given a binary tree and two values p and q, return the value of their lowest common ancestor, the deepest node that has both below it (or is one of them). Recurse. If a node is p or q, return it. Otherwise ask both subtrees. If both sides found something, this node is where p and q split, so it's the answer. If only one did, pass that up.
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 Request Hierarchy Report, a pipeline you can run and download. See every Software Engineer project.
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