说明：  « 问题描述： 按前序列出二叉树各结点为根的子树的结点数。 « 实验任务： 对于给定的二叉树，计算二叉树各结点为根的子树的结点数，并按前序列出。
(« Description of the problem: According to the former sequence of binary tree nodes for each sub-tree root nodes. « Experimental task: For a given binary tree, binary tree calculation for each node of the subtree root nodes, and the former sequence.)