Check Completeness of a Binary Tree LeetCode solution in Python

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class Solution:
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    def isCompleteTree(self, root: Optional[TreeNode]) -> bool:
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        # if not root: return True
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        def node_count(root):
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            if not root:
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                return 0
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            return 1 + node_count(root.left) + node_count(root.right)
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        def isCBT(root, i, count):
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            if not root:
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                return True
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            if i >= count:
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                return False
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            return isCBT(root.left, 2 * i + 1, count) and isCBT(
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                root.right, 2 * i + 2, count
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            )
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        return isCBT(root, 0, node_count(root))