hdu 5073

#include<iostream>
#include<cmath>
#include<cstdio>
#include<vector>
#include<algorithm>
using namespace std;
int n,k;
long double sumxx[50005];
long double sumx2[50005];
long long v[50005];
int main()
{
int T;
cin>>T;
while(T--)
{
cin>>n>>k;
long double sumx=0;
long double summ=n;
for(int i=1;i<=n;i++)
{
cin>>v[i];
}
if(k==n||k==n-1)
{
puts("0");continue;
}
sort(v+1,v+1+n);
for(int i=1;i<=n;i++)
{
sumx=sumx+v[i];
sumxx[i]=sumx;
sumx2[i]=sumx2[i-1]+v[i]*v[i];
}
double anss=sumx2
+n*sumxx
*sumxx
-2*sumxx
/n*sumxx
;
for(int i=0;i<=k;i++)
{
long double tx=sumxx[n-k+i]-sumxx[i];
long double zxin=tx/(n-k);
long double tans=sumx2[n-k+i]-sumx2[i]-2*zxin*tx+(n-k)*zxin*zxin;
if(tans<anss)anss=tans;
}
printf("%.12lf\n",anss);
}
return 0;
}