求二叉树层序遍历

题目描述

给定一个二叉树，返回该二叉树层序遍历的结果，（从左到右，一层一层地遍历）
例如：
给定的二叉树是{3,9,20,#,#,15,7},

 该二叉树层序遍历的结果是
[
[3],
[9,20],
[15,7]
]

输入：{1,2}

输出：[[1],[2]]

import java.util.*;

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

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return int整型ArrayList>
     */
    public ArrayList> levelOrder (TreeNode root) {
        
        // write code here
        ArrayList> result = new ArrayList>();
        if (root == null ){
            return result;
        }
        Queue queue = new LinkedList();
        queue.offer(root);
        while(!queue.isEmpty()){
            ArrayList floor = new ArrayList();
            int len = queue.size();
            for (int i=0; i){
                TreeNode temp = queue.poll();
                floor.add(temp.val);
                if (temp.left !=null){
                    queue.offer(temp.left);
                }
                if (temp.right !=null){
                    queue.offer(temp.right);
                }
            }
            result.add(floor);
        }
        
        return result;
    }
}