4. (18 pts) Write a simple recursive function to calculate (and return) the length of the shortest path (from root to a leaf node) in a given general binary tree T. The length of the shortest path is equal to the number of edges along the path from the root to the highest leaf. See the example below: You can assume the following tree node structure: class Node // this is a fragment; would generally need member functions { Node *pLeft; // points to the left subtree Node *pRight; // points to the right subtree int mData; }; in c++