# LeetCode 637. Average of Levels in Binary Tree

## Description

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

Given the `root` of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within `10-5` of the actual answer will be accepted.

Example 1:

```Input: root = [3,9,20,null,15,7]
Output: [3.00000,14.50000,11.00000]
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].
```

Example 2:

```Input: root = [3,9,20,15,7]
Output: [3.00000,14.50000,11.00000]
```

Constraints:

• The number of nodes in the tree is in the range `[1, 104]`.
• `-231 <= Node.val <= 231 - 1`

## Explanation

Do breadth-first search and calculate average on levels.

## Python Solution

``````# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def averageOfLevels(self, root: TreeNode) -> List[float]:
results = []

queue = []
queue.append(root)

while queue:
size = len(queue)
level = []

for i in range(size):
node = queue.pop(0)

level.append(node.val)

if node.left:
queue.append(node.left)
if node.right:
queue.append(node.right)

results.append(sum(level) / len(level))

return results``````
• Time Complexity: O(N).
• Space Complexity: O(N).