二叉树的基本功能：1.生成一棵以二叉链表存储的二叉树bt (节点树可自定义)2.用递归方法前序、中序、后序遍历bt，并以缩格形式打印bt上各结点的信息3.交换bt上的所有左右子树，并以缩格形式打印出交换前-The basic function of a binary tree: a tree in order to generate a list stored in binary binary bt (node ​ ​ tree can be customized) 2 before using recursive method preorder, inorder, postorder bt, and indent various forms of print bt Information node 3. exchange all around the sub-tree bt, and print out the form to indent before switching