//合并链表 求交集
LinkList Union(LinkList &la,LinkList &lb)
{pa=la->next;pb=lb->next;pc=la;while(pa&&pb){if(pa->data==pb->data){pc->next=pa;pc=pa;pa=pa->next;q=pb;pb=pb->next;free(q);}else if(pa->data<pb->data){q=pa;pa=pa->next;free(q);}else{q=pb;pb=pb->next;free(q);}}while(pa){q=pa;pa=pa->next;free(q);}while(pb){q=pb;pb=pb->next;free(q);}pc->next=NULL;free(lb);return lc;		//空间复杂度1，时间l1+l2
}