Aizu 2300 Calender Colors（暴力）

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<bits/stdc++.h>
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 LOCAL
int 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<<n)-1; S>=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;
}