637-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,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]

My solution：

from collections import deque
# 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: Optional[TreeNode]
        :rtype: List[float]
        """
        if not root:
            return []
        res = []
        queue = deque()
        queue.append(root)
        while queue:
            length = len(queue)
            # sum value is float so that the mean can be calculate to a fload value
            add = 0.0
            for i in range(length):
                cur = queue.popleft()
                add += cur.val
                if cur.left:
                    queue.append(cur.left)
                if cur.right:
                    queue.append(cur.right)
            res.append(add/length)
        return res