def removeNthFromEnd(self, head, n):
        """
        定義兩個指標，表示兩個元素的間隔，間隔大小固定為n-1，兩個指標分別為pre，end
        """
        pre = head
        end = head
        for _ in range(n):
            end = end.next
        if end is None:  # 需要刪除的節點為第一個節點時，即返回第二個節點為頭節點的連結串列
            return head.next
        while end.next is not None:
            pre = pre.next
            end = end.next
        pre.next = pre.next.next 
        return head