题解 | #牛群平均重量#

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[]{};
        }
        List<Double> list = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        int level = 0;
        while(!queue.isEmpty()){
            double sum = 0;
            int size = queue.size();
            for(int i = 0; i < size;i++){
                TreeNode node = queue.poll();
                sum += node.val;

                if(node.left != null){
                    queue.add(node.left);
                }

                if(node.right != null){
                    queue.add(node.right);
                }
            }
            list.add(sum / size);
            level++;
        }
         double [] result = new double[list.size()];
        for (int i = 0; i < list.size(); i++) {
            result[i] = list.get(i);
        }
        return result;
    }
}