三点坐标确定圆心坐标

struct Point
{
    double x,y;
    friend Point operator - (Point a,Point b) //重载友元运算符
    {
        Point temp;
        temp.x = a.x - b.x;
        temp.y = a.y - b.y;
        return temp;
    }
};

Point get_pc1(Point p1, Point p2, Point p3)  //求圆心
{
    double a, b, c, d, e, f;
    Point p;
    a = 2*(p2.x-p1.x);
    b = 2*(p2.y-p1.y);
    c = p2.x*p2.x+p2.y*p2.y-p1.x*p1.x-p1.y*p1.y;
    d = 2*(p3.x-p2.x);
    e = 2*(p3.y-p2.y);
    f = p3.x*p3.x+p3.y*p3.y-p2.x*p2.x-p2.y*p2.y;
    p.x = (b*f-e*c)/(b*d-e*a);
    p.y = (d*c-a*f)/(b*d-e*a);
    r = sqrt((p.x-p1.x)*(p.x-p1.x)+(p.y-p1.y)*(p.y-p1.y));//半径
    return p;
}