hdu 4033 二分几何

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <math.h>
 4 #include <algorithm>
 5 using namespace std;
 6 #define pi acos(-1.0)
 7 #define exp 1e-8
 8 int main()
 9 {
10     int t,n,i,j,flag,cas = 1;
11     double a[105];
12     scanf("%d",&t);
13     while(t--)
14     {
15         scanf("%d",&n);
16         flag = 0;
17         for(i = 0; i<n; i++)
18             scanf("%lf",&a[i]);
19         a[n] = a[0];
20         double l = 0,r = 20000,mid;
21         for(i = 1; i<=n; i++)
22         {
23             r = min(r,a[i]+a[i-1]);
24             l = max(l,fabs(a[i]-a[i-1]));
25         }
26         while(r-l>exp)
27         {
28             mid = (l+r)/2;
29             double s,sum=0;
30             for(i = 1; i<=n; i++)
31             {
32                 s = (a[i]*a[i]+a[i-1]*a[i-1]-mid*mid)/(2.0*a[i]*a[i-1]);
33                 sum+=acos(s);
34             }
35             if(fabs(sum-2*pi)<exp)
36             {
37                 flag = 1;
38                 break;
39             }
40             else if(sum>2*pi)
41                 r = mid;
42             else
43                 l = mid;
44         }
45         printf("Case %d: ",cas++);
46         if(flag)
47             printf("%.3f\n",mid);
48         else
49             printf("impossible\n");
50     }
51 
52     return 0;
53 }