本代码实现二叉树的先序，中序的递归算法及非递归算法，并用递归实现了后序遍历-This code implements the first binary sequence, sequence of recursive algorithms and non-recursive algorithm, and realized after using recursive traversal

二叉树先序遍历，中序遍历，后序遍历的递归非递归实现-Binary preorder, preorder, after preorder recursive non-recursive