1．定义二叉树的链式数据结构。 2．编写函数，创建下图所示的二叉树。 3．编写函数输出二叉树的先序、中序、后序遍历。-1. The definition of binary tree data structure chain. 2. Write a function, create a binary tree as shown in figure below. 3. Write function, the output of the first binary sequence, in o