增加标志位，隔一行进行翻转

import java.util.*;

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        //增加一个标志变换方向
        ArrayList<ArrayList<Integer>> res = new ArrayList<>();
        if(pRoot==null) return res;
        Queue<TreeNode> queue = new LinkedList<>();
        boolean flag = true;
        queue.add(pRoot);
        while(!queue.isEmpty()){
            int size = queue.size();
            ArrayList<Integer> temp = new ArrayList<>();
            for(int i = 0;i < size;i++){
                pRoot = queue.poll();
                if(pRoot.left!=null) queue.add(pRoot.left);
                if(pRoot.right!=null) queue.add(pRoot.right);
                temp.add(pRoot.val);
            }
            if(!flag) Collections.reverse(temp);
            res.add(temp);
            flag = !flag;
            
        }
        return res;
    }

}