二叉树的非递归遍历

　　周末闲来无事，突然想到了二叉树的遍历问题，如果考虑用递归算法的话比较简单，但是如果用空间换取时间的话，考虑用辅助数据结构：栈来解决遍历的问题，代码如下：   

    //非递归后序遍历二叉树
        static void PostOrder(BinaryTreeNode root)
        {
            Stack<BinaryTreeNode> stack = new Stack<BinaryTreeNode>();

          BinaryTreeNode curr = root;
            while (curr != null)
            {
                stack.Push(curr );
                curr = curr .Left;
            }
            BinaryTreeNode tmp = null;
            BinaryTreeNode last = null;
            while (stack.Count > 0)
            {
                tmp = stack.Peek();
                if (tmp.Right == null || tmp.Right == last) //关键点：栈顶元素的右孩子为空或者为刚刚访问过的节点时才弹出并输出
                {
                    tmp = stack.Pop();
                    last = tmp;
                    Console.WriteLine(tmp.Data);
                }
                else
                {
                    tmp = tmp.Right;//右孩子不为空入栈

                    stack.Push(tmp);
                    while (tmp.Left != null)//并将右孩子的所有左子孙节点入栈
                    {
                        stack.Push(tmp.Left);
                        tmp = tmp.Left;
                    }
                }
            }

        }

       //非递归前序遍历二叉树

        static void PrevOrder(BinaryTreeNode root)
        {
            Stack<BinaryTreeNode> stack = new Stack<BinaryTreeNode>();

            stack.Push(root);
            BinaryTreeNode tmp = null;
            while (stack.Count >0)
            {
                tmp = stack.Pop();
                Console.WriteLine(tmp.Data);
                if (tmp.Right != null)
                    stack.Push(tmp.Right); //右孩子节点不为空入栈,因为要先输出左孩子，鉴于栈的特点是先入后出，所以先入右孩子
                if (tmp.Left != null)
                    stack.Push(tmp.Left);//左孩子节点不为空入栈

            }
        }

        //非递归中序遍历二叉树
        static void MiddleOrder(BinaryTreeNode root)
        {
            Stack<BinaryTreeNode> stack = new Stack<BinaryTreeNode>();

           BinaryTreeNode curr = root;
            while (curr!= null)
            {
                stack.Push(curr);
                curr= curr.Left;
            }
            BinaryTreeNode tmp = null;
            while (stack.Count > 0)
            {
                tmp = stack.Pop();//与后续遍历的差别是：输出的时候检测右孩子是否为空，或者右孩子是否刚刚访问过
                Console.WriteLine(tmp.Data);
                tmp = tmp.Right;
                if (tmp != null)
                {
                    stack.Push(tmp);
                    while (tmp.Left != null)
                    {
                        stack.Push(tmp.Left);
                        tmp = tmp.Left;
                    }
                   
                }
            }
        }

测试通过的代码：http://files.cnblogs.com/shiyulun1984/test.rar

欢迎拍砖！