HDU 1969 Pie

#include <stdio.h>
#include <math.h>
const double eps=1e-6;
const double pi=acos(-1.0);
const int N=10010;
double a
;
int n,f;
int ok(double m)
{
int i,cnt=0;
for (i=1;i<=n;i++)
cnt+=(int)(a[i]/m);
return cnt>f;
}
int main()
{
int T,i;
double s,r,l,m;
scanf("%d",&T);
while (T--)
{
s=0;
scanf("%d%d",&n,&f);
for (i=1;i<=n;i++)
{
scanf("%lf",&r);
a[i]=r*r*pi;
s+=a[i];
}
l=0; r=s;
while (r-l>eps)
{
m=(l+r)/2;
if (!ok(m)) r=m;
else l=m;
}
printf("%.4lf\n",l);
}
return 0;
}