Find the lowest common ancestor of two nodes in a binary tree.
Whether you can reason recursively about a tree without drawing the whole thing, and whether you notice what the tree guarantees.
CodingStandard
Who reports being asked this
LinkedIn · Meta · Microsoft
What a strong answer does
The first clarification I would ask is whether this is a binary search tree or just an arbitrary binary tree. If it is a BST, the ordering property makes the problem much simpler: starting at the root, if both target values are smaller than the current node, go left; if both are larger, go right; otherwise the current node is where the paths split, so it is the lowest common ancestor. It is worth saying this out loud because jumping directly to the general-tree recursion can look like missing an important guarantee.