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Average of Levels in Binary Tree

Question​

What is the average value of all nodes at each level of a given Binary Tree?

Example 1
Input: 
    3
   / \
  9  20
    /  \
   15   7

Output: [3, 14.5, 11]

Solution​

all//Average of Levels in Binary Tree.py


# 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):
        if not root:
            return []
        result = []
        queue = [root]
        while queue:
            size = len(queue)
            level_sum = 0
            for i in range(size):
                node = queue.pop(0)
                level_sum += node.val
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
            result.append(level_sum / size)
        return result