hdu 5073

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#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]+n*sumxx[n]*sumxx[n]-2*sumxx[n]/n*sumxx[n];       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;}

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