uva 12097 - Pie

简单题，二分就行；

 #include<cstdio>
 #include<cmath>
 #define pi acos(-1.0)
 #define eps 0.000001
 #define maxn 10009
 using namespace std;
 double area[maxn];

 int main()
 {
     int t,n,f,ri;
     double r=-;
     scanf("%d",&t);
     while(t--)
     {
         scanf("%d%d",&n,&f);
         f=f+;
         for(int i=;i<n;i++)
         {
             scanf("%d",&ri);
             area[i]=ri*ri*pi;
             if(area[i]>r)r=area[i];
         }
         double l=0.0;
         while(r-l>eps)
         {
             double mid=(r+l)/;
             int cnt=;
             for(int i=;i<n;i++)
                 cnt+=floor(area[i]/mid);
             if(cnt>=f)l=mid;
             else r=mid;
         }
         printf("%.4lf\n",l);
     }
     return ;
 }