1. 用二叉链表保存二叉树 2. 以基于二叉树的先序序列创建立二叉树 3. 按前序、中序、后序遍历二叉树（三选一） -1. Using binary tree preservation list 2. Binary Tree-based sequence of the first order to establish a tree 3. According to pre-order, in sequence, after the binary tree traversal (c el