90pts TLE#10#12#13 求调

#include <bits/stdc++.h>
using namespace std;
int n;
double x[19], y[19];
double minn = 1e9;
int b[19];
double f(double xa, double ya, double xb, double yb)//算距离
{
    return sqrt((xa-xb)*(xa-xb)+(ya-yb)*(ya-yb));
}
void dfs(int cnt, double sum, double xn, double yn)//cnt表示已经走过cnt个点,sum表示当前总和为sum且坐标为(xn, yn)
{
    if(cnt == n)
    {
        minn = min(sum, minn);
    }
    if(sum >=minn) return;
    for(int i = 1; i <= n; i++)
    {
        if(b[i] == 0)
        {
            b[i] = 1;
            dfs(cnt+1, sum + f(xn, yn, x[i], y[i]), x[i], y[i]);
            b[i] = 0;
        }
    }
}
int main()
{
    cin >> n;
    for(int i = 1; i <= n; i++) cin >> x[i] >> y[i];
    dfs(0, 0, 0, 0);
    printf("%.2f", minn);
    return 0;    
}