struct st *And(struct st *A,struct st *B)
{
    struct st *pa,*pb,*C,*pc;
    C=(struct st *)malloc(sizeof(struct st));
    pa=A->next;
    pb=B->next;
    C=pc=A;
   

    while(pa)
    {
        pc->next=pb;
        pc=pb;
        pb=pb->next;
        pa=pa->next;
        pc->next=pa;
        pc=pa;
        

    }

   pc->next=pb;
   return(C);
}
不用排序的 输入1，2，3   4,5,6，输出1,4,2,5,3,6

按你的输入方式我编了个，你试试。
struct st *And(struct st *A,struct st *B)
 {
     struct st *pa,*pb,*pc,*pd,*C;
     
     C=pa=A;
     pb=B;
     while(pa->next)
     {
        pc=pa->next;
        pa->next=pb;
        pd=pb->next;
        pb->next=pc;
        pa=pc;
        pb=pd;
     }
     
    return(C);
 }

while(pa->next)要改成while(pa)

是哦。