计算二叉树的直径（二叉树中相距最远的两个节点之间的距离）的算法。-Calculate the diameter of binary tree (binary tree in the farthest away from the distance between two nodes) of the algorithm.

数据结构问题：用c++求解二叉树直径，vs2015及以上版本可直接运行(Solving the diameter of binary trees in c++)