洛谷 P1433 吃奶酪

#include <cstdio>
#include <cmath>
#define N 25

double calc(double x1,double y1,double x2,double y2)
{
    return sqrt((double)(x1-x2)*(x1-x2)+(double)(y1-y2)*(y1-y2));
}
int n;
bool vis[N];
double f[N][N],x[N],y[N],ans=1e9;
double minn(double a,double b) {return a>b?b:a;}
void dfs(int now,int num,double dist)
{
    if(num==n) {ans=minn(ans,dist);return;}
    if(dist>ans) return;
    for(int i=1;i<=n;++i)
    {
        if(now==i||vis[i]) continue;
        vis[i]=1;
        dfs(i,num+1,dist+f[now][i]);
        vis[i]=0;
    }
}
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;++i) scanf("%lf%lf",&x[i],&y[i]),f[0][i]=calc(0,0,x[i],y[i]);
    for(int i=1;i<=n;++i)
     for(int j=i+1;j<=n;++j)
      f[i][j]=f[j][i]=calc(x[i],y[i],x[j],y[j]);
    dfs(0,0,0);
    printf("%.2lf",ans);
    return 0;
}