建立一颗二叉排序树,并对其前序遍历。遍历是对树的一种最基本的运算，所谓遍历二叉树，就是按一定的规则和顺序走遍二叉树的所有结点，使每一个结点都被访问一次，而且只被访问一次。由于二叉树是非线性结构，因此，树的遍历实质上是将二叉树的各个结点转换成为一个线性序列来表示。 -Create a binary sort tree, and the preorder traversal. Tree traversal is a fundamental operation, the so-called traversing a binary tree, that is, according to certain rules and order all over the binary tree all nodes, so that each node have been visited once and once only be accessed . The binary tree is a nonlinear structure, therefore, is essentially a tree traversal the binary tree each node will be converted into a linear sequence to represent.