def removeDuplicates(self, head: Node | None):
    current_node = head
    s = set((current_node.data, ))

    while current_node.next:
        if current_node.next.data not in s:
            s.add(current_node.next.data)
            current_node = current_node.next
        else:
            current_node.next = current_node.next.next

    return head