剑指offer-把二叉树打印成多行

/*从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。*/

import java.awt.List;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

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

    }

}

public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(pRoot);
        while(!queue.isEmpty()) {
            ArrayList<Integer> list = new ArrayList<>();
            int cnt = queue.size();
            while(cnt-->0) {
                TreeNode t = queue.poll();
                if(t==null) continue;
                list.add(t.val);
                queue.add(t.left);
                queue.add(t.right);
            }
            if(list.size()!=0) 
                ret.add(list);
        }
        return ret;
    }
}