链表的合并，先把两个链表中的数据按一定顺序排列，再把相同的数据只保留一个。 两个集合相减则先找出相同的数据，然后将相同的数据删除。 -The combined list, first two lists of data by a certain order, then the same data to retain only one. Subtracting the first two sets to find the same data, and then delete the sam