PP TimDiemPhaiTren(Ref head)
{
	PP max = head->point;
	for (Ref p = head; p; p = p->next)
	if (p->point->y > max->y) max = p->point;
	else if (p->point->y == max->y && p->point->x > max->x) max = p->point;
	return max;
}

double TinhCos(PP p1, PP p2)
{
	double t2, t3;
	int t1;
	t1 = p1->x *p2->x + p1->y *p2->y;
	t2 = sqrt(p1->x *p1->x + p1->y *p1->y);
	t3 = sqrt(p2->x *p2->x + p2->y *p2->y);
	return t1 / (t2*t3);
}

void Find(Ref head, PP &p, PP &p1, PP &v)
{
	double max = -2, temp;
	PP u = new POINT;
	for (Ref c = head; c; c = c->next)
	{
		u->x = c->point->x - p->x;
		u->y = c->point->y - p->y;
		temp = TinhCos(u, v);
		if (temp > max)
		{
			max = temp;
			p1 = c->point;
		}
	}
	v->x = p1->x - p->x;
	v->y = p1->y - p->y;
}
void DaGiacLoi(Ref head)
{
	PP p = NULL, p1 = NULL, v = new POINT;
	p = TimDiemPhaiTren(head);
	printf("\nCau u: Toa do cac dinh cua da giac loi la:\n\t");
	OutputPoint(p);
	p->ok = false;
	v->x = 1;
	v->y = 0;
	do
	{
		Find(head, p, p1, v);
		if (!p1->ok) break;
		OutputPoint(p1);
		p1->ok = false;
		p = p1;
	} while (true);
	printf("\n");
}