Problem: find the common ancestor of two nodes in a tree
Given a "tree" pointer pointing to the root node of a tree and the other two pointers to two nodes in the tree. You are expected to write a C++ subroutine to find the common ancestor of the two nodes. In any unexpected condition, your code should return null pointer and avoid crashing.
For example, if the tree is like below, B is the common ancestor of E and G; A is the common ancestor of H and F; D is the common ancestor of D and G.
You are allowed to use recursion but as few as possible. You are NOT allowed to use STL. Please follow the type definitions shown below:
