637. 二叉树的层平均值

 1 import java.util.ArrayList;
 2 import java.util.LinkedList;
 3 import java.util.List;
 4 import java.util.Queue;
 5 
 6 public class AverageOfLevesInBinaryTree {
 7     static class TreeNode {
 8         int val;
 9         TreeNode left;
10         TreeNode right;
11         TreeNode(int x) {
12             val = x;
13         }
14     }
15     
16     public List<Double> averageOfLevels(TreeNode root) {
17         List<Double> res = new ArrayList<>();
18         if(root == null) {
19             return res;
20         }
21         Queue<TreeNode> queue = new LinkedList<>();
22         queue.add(root);
23         while(!queue.isEmpty()) {
24             int size = queue.size();
25             double sum = 0;
26             for(int i = 0; i < size; i++) {
27                 TreeNode temp = queue.remove();
28                 sum += temp.val;
29                 if(temp.left != null) {
30                     queue.add(temp.left);
31                 }
32                 if(temp.right != null) {
33                     queue.add(temp.right);
34                 }
35             }
36             res.add(sum / size);
37         }
38         return res;
39     }
40 }