实现二叉树链表表示的二叉树：

建立一棵二叉树；

按先序、中序和后序遍历二叉树；

按层次遍历；

求一棵二叉树的高度；

交换一棵二叉树的左右子树；

复制一棵二叉树。-Realize that the binary tree binary tree list: building a binary tree　by the first order, in sequence, and after traversing a binary tree　by level traversal　seek a binary tree of height　exchange of a binary left and right sub-tree tree　copy a binary tree.