Lowest Common Ancestor of a Binary Tree

Question

This is a popular interview question and the only article I can find on the topic is one from TopCoder. Unfortunately for me, it looks overly complicated from an interview answe

Answer 1

Constant space answer: (although not necessarily efficient).

Have a function findItemInPath(int index, int searchId, Node root)

then iterate from 0 .. depth of tree, finding the 0-th item, 1-th item etc. in both search paths.

When you find i such that the function returns the same result for both, but not for i+1, then the i-th item in the path is the lowest common ancestor.