二叉树遍历(Traversal)是指沿着某条搜索路线，依次对树中每个结点均做一次且仅做一次访问。访问结点所做的操作依赖于具体的应用问 题。 遍历是二叉树上最重要的运算之一，是二叉树上进行其它运算之基础。(Two tree traversal (Traversal) refers to a search line, in turn, each node in the tree to do once, and only a visit. The operation of the access nod