1. Lowest Common Ancestor of a Binary Search Tree

2. Lowest Common Ancestor of a Binary Tree

3. CC: Lowest common ancestor of a binary tree

3. Lowest common ancestor of a binary tree

区别是，两个node的其中一个可能不在tree里。

Can use Info class to set a boolean value "isAncestor" to identify the two cases such as that one node is not in the tree.