之字打印二叉树

  public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
            ArrayList<ArrayList<Integer>> datas=new ArrayList<>();
            if (pRoot==null){
                return datas;
            }
            Stack<TreeNode> stack1=new Stack<>(); //存放奇数层结点
            stack1.push(pRoot);
            Stack<TreeNode> stack2=new Stack<>();//存放偶数层结点
            boolean leftToRight=true;//奇数层--从左到右
            while (!stack1.isEmpty()||!stack2.isEmpty()){  //只要树没有遍历完
                ArrayList<Integer> data=new ArrayList<>();
                if (leftToRight==true){ //如果是奇数层
                    //将结点从左到右加入偶数栈
                    while (!stack1.isEmpty())
                    {
                        TreeNode node = stack1.pop(); //取队栈顶元素
                        if (node.left!=null){
                            stack2.push(node.left);
                        }
                        if (node.right!=null){
                            stack2.push(node.right);
                        }
                        data.add(node.val);
                    }
                    leftToRight = false;
                }else {
                    while (!stack2.isEmpty())
                    {
                        TreeNode node = stack2.pop(); //取队栈顶元素
                        if (node.right!=null){
                            stack1.push(node.right);
                        }
                        if (node.left!=null){
                            stack1.push(node.left);
                        }
                        data.add(node.val);
                    }
                    leftToRight=true;
                }
                datas.add(data);
            }
            return datas;
    }