Binary Tree Tilt LeetCode solution in Python

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# Runtime: 66 ms (Top 84.95%) | Memory: 16.4 MB (Top 43.30%)
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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, val=0, left=None, right=None):
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# self.val = val
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# self.left = left
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# self.right = right
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class Solution:
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    def findTilt(self, root: Optional[TreeNode]) -> int:
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        res = [0]
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        def tilt_helper(root, res):
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            if not root:
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                return 0
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            left = tilt_helper(root.left, res)
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            right = tilt_helper(root.right, res)
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            res[0] += abs(left - right)
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            return left + right + root.val
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        tilt_helper(root, res)
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        return res[0]