以二叉链表表示二叉树，实现二叉树先序遍历、中序遍历、后序遍历的递归算法；直接利用栈的基本操作，实现二叉树先序遍历的非递归算法。-Binary list, binary tree, Binary Tree, Inorder traversal, recursive algorithm after preorder　direct use of the basic operation of the stack, the non-recursive algorithm Binary Tree.