# 637. Average of Levels in Binary Tree

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Example 1:

```Input:
3
/
9  20
/
15   7
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].```

Note:

1. The range of node’s value is in the range of 32-bit signed integer.

Java代码如下：

```/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/

import java.util.*;

public class Solution {
public List averageOfLevels(TreeNode root) {
List result = new LinkedList();
List list = new LinkedList();

while(!list.isEmpty()) {
int size = list.size();
double sum = 0.0;

for(int i = 0; i < size; i++) {
TreeNode node = list.get(0);
sum += node.val;
if(node.left != null) {
}
if(node.right != null) {
}
list.remove(node);
}

double avg = sum / size;
}
return result;
}
}```

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