[Python-leetcode637- width tree traversal of a binary tree average layer]

Given a non-null binary tree, each node returns an array of the average value thereof.

Example 1:

Input:
3
/ \
920
    / \
  157
Output: [3, 14.5, 11]
Explanation:
average value of 0 is 3 layer, the first layer 14.5, the second layer 11 is thus returned [3, 14.5, 11]
Note:

Node value in a range of 32-bit signed integer within the range.

 

# 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