HDU 1969

 1 #include <iostream>
 2 #include <cmath>
 3 #include <algorithm>
 4 #include <stdio.h>
 5 using namespace std;
 6 
 7 
 8 int main()
 9 {
10     int T;
11     cin>>T;
12     for(int test = 0;test<T;test++)
13     {
14     int N,F;
15     cin>>N>>F;
16     F+=1;
17 
18     int* Radius = new int[N];
19     double* Pie = new double[N];
20     for(int i =0;i<N;i++)
21     {
22     cin>>Radius[i];
23     Pie[i] = Radius[i]*Radius[i]*acos(-1.0);
24     }
25 
26     sort(Pie,Pie+N);
27 
28     double high = Pie[N-1];
29     double low = 0;
30 
31     while(high-low>1e-5)
32     {
33         double mid = (high + low)/2.0;
34         bool isEnough = false;
35         int num = 0;
36         for(int j =0; j<N ; j++)
37         {
38             num+=(int)(Pie[j]/mid);
39        }
40          isEnough = (num>=F);
41         if(isEnough)
42         {
43             low = mid;
44         }else
45         {
46         high = mid;
47         }
48     }
49     printf("%.4lf\n",(high+low)/2.0);
50     }
51 
52     return 0;
53 }