UVALive 7066 Intersection 求圆环面积并

稍微分析一下就出来了！就是求两个圆环的面积并！

当两个圆环的圆心的距离d>=2*R, s=0;

d>=2*r时，s=area(R,R)-area(R,r)*2;

d<2*r时，s=area(R,R)-area(R,r)*2+area(r,r);

#include <iostream>
#include<stdio.h>
#include<cmath>
#include<iomanip>
#include<algorithm>
using namespace std;
double area(double x,double y,double r,double xx,double yy,double rr)
{
double s,t,t1;
double d=sqrt((x-xx)*(x-xx)+(y-yy)*(y-yy));
if(d>=r+rr) s=0;
else if(d<=fabs(r-rr))
s=min(acos(-1.0)*r*r,acos(-1.0)*rr*rr);
else
{
t=(r*r+d*d-rr*rr)/2.0/d;
t1=sqrt(r*r-t*t);
s=-d*t1+r*r*acos(t/r)+rr*rr*acos((d-t)/rr);
}
return s;
}
int main()
{
int t,kcase=1;
double x1,x2,y1,y2,r1,r2;
scanf("%d",&t);
while(t--)
{
scanf("%lf%lf",&r1,&r2);
scanf("%lf%lf",&x1,&y1);
scanf("%lf%lf",&x2,&y2);
double ans;
ans=area(x1,y1,r2,x2,y2,r2)+area(x1,y1,r1,x2,y2,r1)-2*area(x1,y1,r1,x2,y2,r2);
printf("Case #%d: %.6lf\n",kcase++,ans);
}
return 0;
}