题解 | #求二叉树的层序遍历#

题目地址

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<ArrayList<>>
     */
    public ArrayList<ArrayList<Integer>> levelOrder (TreeNode root) {
        // write code here
        Queue<TreeNode> q = new LinkedList();
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        q.offer(root);
        while(!q.isEmpty()){
            int len = q.size();
            ArrayList<Integer> list = new ArrayList<>();
            for(int i = 0;i<len;i++){
                TreeNode temp = q.poll();
                list.add(temp.val);
                if(temp.left != null){
                    q.offer(temp.left);
                }
                if(temp.right != null){
                    q.offer(temp.right);
                }
            }
            result.add(list);
        }
        return result;
    }
}