牛客网：NC80 把二叉树打印成多行

import java.util.*;
import java.util.ArrayList;



public class Solution {
    ArrayList > Print(TreeNode root) {
         ArrayList> res = new ArrayList<>();
        if (root == null){
            return res;
        }
       
        Deque queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()){
            int size = queue.size();
            ArrayList temp = new ArrayList();
            for (int i = 0; i < size; i++){
                TreeNode node = queue.poll();
                temp.add(node.val);
                if (node.left != null){
                    queue.offer(node.left);
                }
                if (node.right != null){
                    queue.offer(node.right);
                }
            }
            res.add(temp);
        }
        return res;
    }
    
}