按照广度遍历去处理二叉树，但是对于每一层，设置一个布尔变量，来处理是否从右到左打印。

//如果为空节点，返回空的集合
        if(pRoot == null) return new ArrayList<ArrayList<Integer>>();
        //初始化一个双层链表
        ArrayList<ArrayList<TreeNode>> list = new ArrayList<ArrayList<TreeNode>>();
        ArrayList<TreeNode> listFloor = new ArrayList<TreeNode>();//每一层
        listFloor.add(pRoot);//从左至右广度遍历
        list.add(listFloor);
        boolean leftToRight = true;//从右到左
        while(listFloor.size() != 0)
        {
            ArrayList<TreeNode> listNextFloor = new ArrayList<TreeNode>();//Z型遍历
            for(TreeNode treeNode : listFloor)
            {
                if(treeNode.left != null)
                {
                    listNextFloor.add(treeNode.left);
                }
                if(treeNode.right != null)
                {
                    listNextFloor.add(treeNode.right);
                }
            }
            if(listNextFloor.size() != 0)
            {
                //颠倒顺序
                if(leftToRight)
                {
                    ArrayList<TreeNode> leftToRightList = new ArrayList<TreeNode>();
                    for(int i = listNextFloor.size() - 1;i >= 0;i --)
                    {
                        leftToRightList.add(listNextFloor.get(i));
                    }
                    leftToRight = false;
                    list.add(leftToRightList);
                }
                else
                {
                    leftToRight = true;
                    list.add(listNextFloor);
                }
            }       
            listFloor = listNextFloor;
        }
        //将list里的值取出来
        ArrayList<ArrayList<Integer>> treeNodeValList = new ArrayList<ArrayList<Integer>>();
        for(ArrayList<TreeNode> treeList : list)
        {
            ArrayList<Integer> IntegerList = new ArrayList<Integer>();
            for(TreeNode treeNode : treeList)
            {
                IntegerList.add(treeNode.val);
            }
            treeNodeValList.add(IntegerList);
        }
        return treeNodeValList;