leetcode1161 Maximum Level Sum of a Binary Tree

"""
BFS遍历题，一遍AC
Given the root of a binary tree, the level of its root is 1, the level of its children is 2, and so on.
Return the smallest level X such that the sum of all the values of nodes at level X is maximal.
Example 1:
Input: [1,7,0,7,-8,null,null]
Output: 2
Explanation:
Level 1 sum = 1.
Level 2 sum = 7 + 0 = 7.
Level 3 sum = 7 + -8 = -1.
So we return the level with the maximum sum which is level 2.
"""
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def maxLevelSum(self, root):
        if root == None:
            return 0
        queue = []
        res = []
        queue.append(root)
        while queue:
            n = len(queue)
            sum = 0
            newqueue = []
            for _ in range(n):
                x = queue.pop(0)
                sum += x.val
                if x.left != None:
                    newqueue.append(x.left)
                if x.right != None:
                    newqueue.append(x.right)
            queue = newqueue
            res.append(sum)
        return res.index(max(res))+1