状压以后，直接暴力枚举，2^20约等于1e6，而且满足bitcount = m的状态很少。

#include
     
      using namespace std;const int maxn = 20+1;double x[maxn],y[maxn],z[maxn];double d[maxn][maxn];double squ(double x) { return x*x; }double dist(int i,int j) { return squ(x[i]-x[j])+squ(y[i]-y[j])+squ(z[i]-z[j]); }//#define LOCALint main(){#ifdef LOCAL    freopen("in.txt","r",stdin);#endif    int n,m; scanf("%d%d",&n,&m);    for(int i = 0; i < n; i++){        scanf("%lf%lf%lf",x+i,y+i,z+i);    }    for(int i = 0; i < n; i++){        for(int j = 0; j < i; j++){            d[i][j] = dist(i,j);        }    }    double ans = 0;    int vc[maxn];    for(int S = (1<
      
       =0; S--){        int c = 0;        for(int i = 0; i < n; i++){            if(S>>i&1) vc[c++] = i;        }        if(c == m){            double sum = 0;            for(int i = 0; i < c; i++){                int a = vc[i];                for(int j = 0; j < i; j++){                    sum += d[a][vc[j]];                }            }            ans = max(ans,sum);        }    }    printf("%lf\n",ans);    return 0;}