leetcode 637 python3 76ms 二叉树的层平均值

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

from collections import deque

class Solution:
    def averageOfLevels(self, root):
        """
        :type root: TreeNode
        :rtype: List[float]
        """
        res = []
        q = deque([root])
        while q:
            curr_sum = 0
            node_num_this_layer = len(q)
            for i in range(0, node_num_this_layer):
                node = q.popleft();
                curr_sum += node.val
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
            res.append(1.0*curr_sum/node_num_this_layer)
        return res