Reverse first k elements of linked list.

void kreverse(int len)

{

      node *st=start,*p=start,*q=p->next,*r=q->next;

      int i=0;

      while(i<len)

      {

            i++;

            q->next=p;

            p=q;

            q=r;

            r=r->next;

      }

      st->next=q;

      start=p;

}