用递归方法分别先序、中序和后序遍历二叉树。动态显示二叉树的建立过程。 步骤：定义二叉树的结构体，开辟空间，构建二叉树。编写子函数，遍历构建的二叉树。 -A recursive first order, respectively, in order, and post-order traversal binary tree. Dynamic display binary tree building process. Steps: definition of binary tree str