1161. 最大層内元素和 （二叉樹的層序周遊）

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def maxLevelSum(self, root: Optional[TreeNode]) -> int:
        queue = collections.deque()
        queue.append(root)

        level = 0
        bigest_sum = root.val
        bigest_level = 1
        while queue:
            level += 1
            level_sum = 0
            length = len(queue)
            for i in range(length):
                rt = queue.popleft()
                if rt.left: queue.append(rt.left)
                if rt.right: queue.append(rt.right)
                level_sum += rt.val
            if level_sum > bigest_sum:
                bigest_sum = level_sum
                bigest_level = level

        return bigest_level