Binary Search Tree to Greater Sum Tree LeetCode solution in Python

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# Runtime: 36 ms (Top 83.6%) | Memory: 16.39 MB (Top 54.5%)
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class Solution:
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    def bstToGst(self, root):
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        self.total = 0
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        def dfs(n):
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            if n:
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                dfs(n.right)
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                self.total += n.val
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                n.val = self.total
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                dfs(n.left)
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        dfs(root)
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        return root