leetcode1161 Maximum Level Sum of a Binary Tree

 1 """
 2 BFS遍历题，一遍AC
 3 Given the root of a binary tree, the level of its root is 1, the level of its children is 2, and so on.
 4 Return the smallest level X such that the sum of all the values of nodes at level X is maximal.
 5 Example 1:
 6 Input: [1,7,0,7,-8,null,null]
 7 Output: 2
 8 Explanation:
 9 Level 1 sum = 1.
10 Level 2 sum = 7 + 0 = 7.
11 Level 3 sum = 7 + -8 = -1.
12 So we return the level with the maximum sum which is level 2.
13 """
14 class TreeNode:
15     def __init__(self, x):
16         self.val = x
17         self.left = None
18         self.right = None
19 
20 class Solution:
21     def maxLevelSum(self, root):
22         if root == None:
23             return 0
24         queue = []
25         res = []
26         queue.append(root)
27         while queue:
28             n = len(queue)
29             sum = 0
30             newqueue = []
31             for _ in range(n):
32                 x = queue.pop(0)
33                 sum += x.val
34                 if x.left != None:
35                     newqueue.append(x.left)
36                 if x.right != None:
37                     newqueue.append(x.right)
38             queue = newqueue
39             res.append(sum)
40         return res.index(max(res))+1