dfs | 洛谷 | P1433

#include <bits/stdc++.h>
#define FF(a,b) for(int a=0;a<b;a++)
#define F(a,b) for(int a=1;a<=b;a++)
#define LEN 20
#define INF 1000000
#define bug(x) cout<<#x<<"="<<x<<endl;

using namespace std;

typedef struct pt{
	pt(double x=0,double y=0):x(x),y(y){}
	double x,y;
}pt;

double pt_dist[LEN][LEN];
int N;
pt npt[LEN];
double ans=INF;
int vis[LEN];

inline double p2(double x){
    return x*x;
}

inline double dist(const pt& a,const pt& b){
    return sqrt(p2(a.x-b.x)+p2(a.y-b.y));
}

void init_dist(){
    F(i,N)
        pt_dist[0][i]=pt_dist[i][0]=dist(pt(0,0),npt[i]);
    for(int i=1;i<=N;i++){
        for(int j=i;j<=N;j++){
            pt_dist[i][j]=pt_dist[j][i]=dist(npt[i],npt[j]);
        }
    }
}

void dfs(int t,int c,double sum){//当前步骤, 当前点,当前和
    if(sum>ans) return;
    if(t>=N){
        ans=min(ans,sum);
        return;
    }
    vis[c]=1;
//    if(t==N) dfs(t+1,0,sum);
//    else
        F(i,N) if(!vis[i]){
            dfs(t+1,i,sum+pt_dist[c][i]);
        }
    vis[c]=0;
}

int main()
{
    freopen("./in","r",stdin);
    scanf("%d",&N);//读入点数
    F(i,N)
        scanf("%lf%lf",&npt[i].x,&npt[i].y);
    init_dist();
    dfs(0,0,0);
    printf("%.2f",ans);
    return 0;
}