[Leet Code] Average of Levels In Binary Tree

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

Problem:

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].

Solution:

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def averageOfLevels(self, root):
        """
        :type root: TreeNode
        :rtype: List[float]
        """
        if root:
            elements = [[root.val]]
            stack = [root]
            self.helper(stack, elements)
            answer_arr = []
            for i in elements:
                answer = 0.00
                for j in i:
                    answer += j
                answer_arr.append(answer / len(i))
                
            return answer_arr
        return root
    def helper(self, stack, elements):
        while len(stack) > 0:
            values = []
            length = len(stack)
            for i in range(length):
                node = stack.pop(0)
                if node.left:
                    values.append(node.left.val)
                    stack.append(node.left)
                if node.right:
                    values.append(node.right.val)
                    stack.append(node.right)
            if values != []:
                elements.append(values)