求两圆相交面积模板

#define PI 3.141592654
#define eps 1e-8

double getdis(int x1,int y1,int x2,int y2){
    return sqrt((double)(x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
}
double getarea(int x1,int y1,double r1,int x2,int y2,double r2){
    double d=getdis(x1,y1,x2,y2);
    if(r1+r2<d+eps) return 0;
    if(d<fabs(r1-r2)+eps){
        double r=min(r1,r2);
        return PI*r*r;
    }
    double x=(d*d+r1*r1-r2*r2)/(2*d);
    double t1=acos(x/r1);
    double t2=acos((d-x)/r2);
    return r1*r1*t1+r2*r2*t2-d*r1*sin(t1);
}

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