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.

# Definition for a binary tree node.
class TreeNode:
     def __init__(self, x):
         self.val = x
         self.left = None
         self.right = None

class Solution:
    def averageOfLevels(self, root):
        """
        :type root: TreeNode
        :rtype: List[float]
        """
        if root is None:
            return []
        temp = [root]
        res = []
        while len(temp):
            l = len(temp)
            ans = 0
            for _ in range(l):
                ans += temp[0].val
                if temp[0].left:
                    temp.append(temp[0].left)
                if temp[0].right:
                    temp.append(temp[0].right)
                temp.pop(0)
            res.append(ans/l)
        return res