二叉树的先序+中序+后序的非递归遍历实现

//先序遍历
    public static void xianxubianli(Node head)
    {
        if(head!=null)
        {
            Stack<Node> tool = new Stack<TreeProblem.Node>();
            tool.add(head);
            //当工具栈不为空时
            while(!tool.isEmpty())
            {
                //取出栈顶元素进行打印
                head = tool.pop();
                System.out.print(head.value+"    ");
                if(head.right!=null)
                    tool.push(head.right);
                if(head.left!=null)
                    tool.push(head.left);
            }
        }
    }

//中序遍历
    public static void zhongxubianli(Node head)
    {
        if(head!=null)
        {
            Stack<Node>p = new Stack<TreeProblem.Node>();
            while(!p.isEmpty()||head!=null)
            {
                if(head!=null)
                {
                    p.push(head);
                    head=head.left;
                }
                    else {
                    head = p.pop();
                    System.out.print(head.value+"    ");
                    head = head.right;
                }
            }
        }
    }

public static void houxubianli(Node head)
    {
        if(head!=null)
        {
            Stack<Node>p1 = new Stack<TreeProblem.Node>();
            Stack<Node>p2 = new Stack<TreeProblem.Node>();
            p1.push(head);
            while(!p1.isEmpty())
            {
                head = p1.pop();
                p2.push(head);
                if(head.left!=null)
                    p1.push(head.left);
                if(head.right!=null)
                    p1.push(head.right);
            }
            while(!p2.isEmpty())
            {
                System.out.print(p2.pop().value+"    ");
            }
        }
    }