//相等则返回true
public static bool Compare(Vertex a, Vertex b)
{
return a.x == b.x && a.y == b.y;
}
//��뾶
private double dis_2(Vertex from, Vertex to)
{
return ((from.x - to.x) * (from.x - to.x) + (from.y - to.y) * (from.y - to.y));
}