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
