hdu 5120 Intersection

http://acm.hdu.edu.cn/showproblem.php?pid=5120

题意：求两个圆环的相交面积。

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <cmath>

 4 #include <algorithm>

 5 using namespace std;

 6 

 7 int t;

 8 double r,R;

 9 struct point

10 {

11     double x,y;

12     double r;

13 };

14 

15 double circle_area(point a,point b)

16 {

17     double s,d,t,t1;

18     d=sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));

19     if(d>=a.r+b.r) s=0;

20     else if(d<=fabs(a.r-b.r)) s=min(acos(-1.0)*a.r*a.r,acos(-1.0)*b.r*b.r);

21     else

22     {

23         t=(a.r*a.r+d*d-b.r*b.r)/2.0/d;

24         t1=sqrt(a.r*a.r-t*t);

25         s=-d*t1+a.r*a.r*acos(t/a.r)+b.r*b.r*acos((d-t)/b.r);

26     }

27     return s;

28 }

29 

30 int main()

31 {

32     scanf("%d",&t);

33     for(int cas=1; cas<=t; cas++)

34     {

35         scanf("%lf%lf",&r,&R);

36         point st1,st2,st3,st4;

37         double x,y;

38         scanf("%lf%lf",&x,&y);

39         st1.x=st2.x=x;

40         st1.y=st2.y=y;

41         st1.r=r;

42         st2.r=R;

43         scanf("%lf%lf",&x,&y);

44         st3.x=st4.x=x;

45         st3.y=st4.y=y;

46         st3.r=r;

47         st4.r=R;

48         double ans=0;

49         ans+=circle_area(st2,st4);

50         ans-=circle_area(st1,st4);

51         ans-=circle_area(st2,st3);

52         ans+=circle_area(st1,st3);

53         printf("Case #%d: %.6lf\n",cas,ans);

54     }

55     return 0;

56 }

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