Cylinder

http://acm.sdut.edu.cn/sdutoj/problem.php?action=showproblem&problemid=2374

思路：三分枚举。

 1 #include <cstdio>

 2 #include <cmath>

 3 #include <cstring>

 4 #include <algorithm>

 5 #define maxn 1000100

 6 using namespace std;

 7 const double eps=1e-12;

 8 const double pi=acos(-1.0);

 9 

10 double w,h;

11 

12 double ok(double x,int flag)

13 {

14     double max1=0;

15     double k=h;

16     double s=w;

17     double r=(x>s)?s:x;

18     double ss=pi*(r/2)*(r/2);

19     double ll=pi*r;

20     double c=k-x;

21     double r1=(k-x)>s?s:(k-x);

22     if(s>=ll&&flag==1)

23     {

24         double v1=ss*c;

25         max1=max(max1,v1);

26     }

27     if(c>=ll&&flag==2)

28     {

29         double v2=ss*s;

30         max1=max(max1,v2);

31     }

32     double s1=pi*(r1/2)*(r1/2);

33     double l1=pi*r1;

34     if(s>=l1&&flag==1)

35     {

36         double v3=s1*x;

37         max1=max(v3,max1);

38     }

39     if(x>=l1&&flag==2)

40     {

41         double v4=s1*s;

42         max1=max(max1,v4);

43     }

44     return max1;

45 }

46 

47 

48 int main()

49 {

50     while(scanf("%lf%lf",&w,&h)!=EOF)

51     {

52         if(w==0&&h==0) break;

53         double l=0,r=h;

54         double ans=0,ans1=0;

55         while(r-l>eps)

56         {

57             double mid1=(r+l)/2;

58             double mid2=(l+mid1)/2;

59             if(ok(mid1,1)>=ok(mid2,1))

60             {

61                 ans=mid1;

62                 l=mid2;

63             }

64             else

65                 r=mid1;

66         }

67         l=0,r=w;

68         while(r-l>eps)

69         {

70             double mid1=(r+l)/2;

71             double mid2=(l+mid1)/2;

72             if(ok(mid1,2)>=ok(mid2,2))

73             {

74                 ans1=mid1;

75                 l=mid2;

76             }

77             else

78                 r=mid1;

79         }

80         printf("%.3lf\n",max(ok(ans,1),ok(ans1,2)));

81     }

82     return 0;

83 }

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