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