zstu-4243 牛吃草

贴一发两圆相交面积模板

 #include<bits/stdc++.h>
 #define pi acos(-1.0)
 using namespace std;
 const double eps=1e-;
 double _abs(double x)
 {
     if(x<) return -x;
     else return x;
 }
 struct point
 {
     point(double _x=,double _y=){x=_x; y=_y;}
     double x,y;
 }p1,p2;
 double R;
 double AREA(point a, double r1, point b, double r2)
 {
     double d=sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
     if(d>=r1+r2) return ;
     if(r1>r2)
     {
         double tmp=r1;
         r1=r2;
         r2=tmp;
     }
     if(r2-r1>=d)
         return pi*r1*r1;
     double ang1=acos((r1*r1+d*d-r2*r2)/(*r1*d));
     double ang2=acos((r2*r2+d*d-r1*r1)/(*r2*d));
     return ang1*r1*r1+ang2*r2*r2-r1*d*sin(ang1);
 }
 int main()
 {
     int T; scanf("%d",&T);
     while(T--)
     {
         scanf("%lf%lf%lf%lf%lf",&p1.x,&p1.y,&p2.x,&p2.y,&R);
         double l=,r=,area=pi*R*R/;
         while(_abs(l-r)>eps)
         {
             double mid=(l+r)/;
             if(AREA(p1,R,p2,mid)>=area) r=mid;
             else l=mid;
         }
         printf("%.4f\n",l);
     }
     return ;
 }