创建一棵二叉树，采用前序遍历的方法建立一棵树，传递的参数为一个指向结点的指针的指针，目的是为了解决传值的问题，输入@符号的时候，表示一棵子树结束线索化二叉树，寻找当前结点的后继结点，寻找当前结点的前驱结点，中序遍历

-create a binary tree using preorder before the establishment of a tree. transmission parameters of a point to the node pointer, the purpose is to solve the problem of traditional values, the importation of the @ symbol, said the end of a tree-binary tree of clues to find the current node's successor nodes, for the current node precursor nodes, China preorder