Convert Sorted List to Binary Search Tree LeetCode solution in Python

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class Solution:
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    def sortedListToBST(self, head: Optional[ListNode]) -> Optional[TreeNode]:
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        arr = []
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        while head:
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            arr.append(head.val)
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            head = head.next
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        def dfs(left, right):
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            if left > right:
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                return
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            m = (left + right) // 2
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            return TreeNode(arr[m], dfs(left, m - 1), dfs(m + 1, right))
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        return dfs(0, len(arr) - 1)