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class Solution:
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    def isPalindrome(self, head: "Optional[ListNode]") -> bool:
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        if head.next == None:
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            return True  # if only 1 element, it's always a palindrome
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        forward = head
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        first_half = []
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        fast = head
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        while fast != None and fast.next != None:
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            first_half.append(forward.val)
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            forward = forward.next
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            fast = fast.next.next
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        # forward should now be through half the list
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        if fast != None:
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            forward = forward.next  # if length isn't even, skip the middle number
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        reverse = len(first_half) - 1
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        while forward != None:
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            if forward.val != first_half[reverse]:
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                return False
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            forward = forward.next
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            reverse -= 1
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        return True