POJ 2546 Circular Area（两个圆相交的面积）

 1 #include <cstdio>
 2 #include <cmath>
 3 #include <cstdlib>
 4 #define PI 3.1415926535897932384626433
 5 
 6 double insection(double x1,double y1,double x2,double y2,double r1,double r2)
 7 {
 8     double distance=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
 9     //相离
10     if(r1+r2<distance) return 0.0 ;
11     //内含
12     else if(abs(r2-r1) >= distance)
13     {
14         if(r2>=r1) return PI*r1*r1;
15         else return PI*r2*r2;
16     }
17     //相交
18     else
19     {
20         double angle1=2*acos((r1*r1+distance*distance-r2*r2)/2/r1/distance);
21         double angle2=2*acos((r2*r2+distance*distance-r1*r1)/2/r2/distance);
22         double ans=r1*r1*angle1/2+r2*r2*angle2/2-r1*r1*sin(angle1)/2-r2*r2*sin(angle2)/2;
23         return ans ;
24     }
25     return 0 ;
26 }
27 int main()
28 {
29     double x1,y1,r1,x2,y2,r2 ;
30     while(~scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&r1,&x2,&y2,&r2))
31     {
32         double ans = insection(x1,y1,x2,y2,r1,r2) ;
33         printf("%.3lf\n",ans) ;
34     }
35     return 0;
36 }