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。

在获取子节点之前的队列大小就是当前层的节点个数

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 {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
         ArrayList<ArrayList<Integer>> layers = new ArrayList<ArrayList<Integer>>();
        if (pRoot == null)
            return layers;
        Deque<TreeNode> queue = new LinkedList<TreeNode>();
        
        queue.offer(pRoot);
        
        while (!queue.isEmpty()) {
            ArrayList<Integer> layer = new ArrayList<Integer>();
            int cur = 0, size = queue.size();
            while (cur < size) {
                TreeNode node = queue.poll();
                layer.add(node.val);
                if (node.left != null) {
                    queue.offer(node.left);
                }
                if (node.right != null) {
                    queue.offer(node.right);
                }
                cur ++;
            }
            layers.add(layer);
        }
        return layers;
    }
    
}