def reverseList(self, head: ListNode) -> ListNode:
        stack = []
        while head:
            stack.append(head)
            head = head.next
        prev = None
        r = None
        while stack:
            curr = stack.pop()
            curr.next = None
            if not prev:
                prev = curr
                r = curr
            else:
                prev.next = curr
                prev = curr
        return r