题解 | #牛群平均重量#

也是对于二叉树层次遍历的考察。在层次遍历的时候，当遍历完每一层后计算出该层的平均值就可以解决了。

完整Java代码如下所示

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 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @return double浮点型一维数组
     */
    public double[] averageOfLevels (TreeNode root) {
        // write code here
        if (root == null) {
            return new double[] {};
        }
        Queue<TreeNode> q = new LinkedList<>();
        List<Double> list = new ArrayList<>();
        q.offer(root);
        while (!q.isEmpty()) {
            int size = q.size();
            double sum = 0;
            for (int i = 0; i < size; i++) {
                TreeNode node = q.poll();
                if (node.left != null) {
                    q.offer(node.left);
                }
                if (node.right != null) {
                    q.offer(node.right);
                }
                sum += node.val;
            }
            list.add(sum / size);
        }
        double[] res = new double[list.size()];
        for (int i = 0; i < list.size(); i++) {
            res[i] = list.get(i);
        }
        return res;
    }
}