4.7 Design an algorithm and write code to find the first common ancestor of two nodes in a binary tree. Avoid storing additional nodes in a data structure. NOTE: This is not necessarily a binary search tree.
LeetCode上的原题，请参见我之前的博客Lowest Common Ancestor of a Binary Tree 二叉树的最小共同父节点。
本文转自博客园Grandyang的博客，原文链接：二叉树的最小共同父节点[CareerCup] 4.7 Lowest Common Ancestor of a Binary Search Tree ，如需转载请自行联系原博主。
