两圆相交面积

//求两圆相交的面积
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<algorithm>
#define esp 1e-8using namespace std;struct Circle{double x,y;double r;
}p[3000];
int cmp(Circle ta,Circle tb)
{return ta.x<tb.x;
}
double calArea(Circle c1, Circle c2)
{double d;double s,s1,s2,s3,angle1,angle2,temp;d=sqrt((c1.x-c2.x)*(c1.x-c2.x)+(c1.y-c2.y)*(c1.y-c2.y));if(d>=(c1.r+c2.r))//两圆相离return 0;if((c1.r-c2.r)>=d)//两圆内含,c1大return acos(-1.0)*c2.r*c2.r;if((c2.r-c1.r)>=d)//两圆内含,c2大return acos(-1.0)*c1.r*c1.r;angle1=acos((c1.r*c1.r+d*d-c2.r*c2.r)/(2*c1.r*d));angle2=acos((c2.r*c2.r+d*d-c1.r*c1.r)/(2*c2.r*d));s1=angle1*c1.r*c1.r;s2=angle2*c2.r*c2.r;s3=c1.r*d*sin(angle1);s=s1+s2-s3;return s;
}int main()
{double ans=0;int n,r;cin>>n>>r;for(int i=1;i<=n;i++)scanf("%lf",&p[i].x),p[i].r=r,p[i].y=0;sort(p+1,p+n+1,cmp);ans=n*acos(-1.0)*r*r;for(int i=1;i<n;i++)ans-=calArea(p[i+1],p[i]);printf("%.12lf\n",ans);return 0;
}