LeetCode 637. 二叉树的层平均值(Average of Levels in Binary Tree)

637. 二叉树的层平均值

637. Average of Levels in Binary Tree

LeetCode637. Average of Levels in Binary Tree

题目描述

给定一个非空二叉树, 返回一个由每层节点平均值组成的数组.

示例 1:

输入:

    3
   / \
  9  20
    /  \
   15   7

输出: [3, 14.5, 11]

解释:

第 0 层的平均值是 3,第 1 层是 14.5,第 2 层是 11.因此返回 [3, 14.5, 11].

注意:

1. 节点值的范围在32位有符号整数范围内。

Java 实现

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

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> result = new LinkedList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if (root == null) {
            return result;
        }
        queue.offer(root);
        while (!queue.isEmpty()) {
            double avg = 0.0;
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                if (queue.peek().left != null) {
                    queue.offer(queue.peek().left);
                }
                if (queue.peek().right != null) {
                    queue.offer(queue.peek().right);
                }
                avg += queue.poll().val;
            }
            result.add(avg / size);
        }
        return result;
    }
}

相似题目

• 102. 二叉树的层次遍历
• 429. N叉树的层序遍历

参考资料

• https://leetcode-cn.com/problems/average-of-levels-in-binary-tree/
• https://leetcode.com/problems/average-of-levels-in-binary-tree/