【python-leetcode637-树的宽度遍历】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

class Solution:
    def averageOfLevels(self, root: TreeNode) -> List[float]:
        if  not root:
            return []
        queue=[root]
        res=[]
        while queue:
            s=0
            l=len(queue)
            for i in range(l):
                t=queue.pop(0)
                s+=t.val
                if t.left:
                    queue.append(t.left)
                if t.right:
                    queue.append(t.right)
            res.append(float(s)/float(l))
        return res