bfs using delimiter
\n# Definition for a binary tree node.\n# class TreeNode:\n#     def __init__(self, x):\n#         self.val = x\n#         self.left = None\n#         self.righ
```\n# Definition for a binary tree node.\n# class TreeNode:\n#     def __init__(self, x):\n#         self.val = x\n#         self.left = None\n#         self.right = None\n\nclass Solution:\n    def maxLevelSum(self, root: TreeNode) -> int:\n        \n        def maxsum(root):\n            \n            if root == None:\n                return 1\n            Q = [root, None]\n            \n            mx = 0\n            lvl = 1\n            lvln = 1\n            lsum = 0\n            while Q != []:\n                p = Q.pop(0)\n                if p == None :\n                    if Q != []:\n                        Q.append(None)\n                \n                    if lsum > mx:\n                        mx = lsum\n                        lvl = lvln\n                    lsum = 0\n                    lvln +=1\n                else:\n                    if p.left != None:\n                        Q.append(p.left)\n                    if p.right != None:\n                        Q.append(p.right)\n                    lsum += p.val\n            return lvl\n                \n        return maxsum(root)\n                    \n                    \n                \n            \n```
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