洛谷OJ 1433 吃奶酪 暴力dfs(最优性cut)

#include <bits/stdc++.h> 
using namespace std;
typedef pair<int,double> pii;
const int N=2e3+20;
const double inf=1e7;
struct node{
    double x,y;
}a[N];
int n;
double d(int i,int j)
{
    double dx=a[i].x-a[j].x;
    double dy=a[i].y-a[j].y;
    return sqrt(dx*dx+dy*dy);
}
double ans,mn;
double dist[N][N];
int vis[N];
void dfs(int cur,double sum,int cnt)
{
    if(sum+(n-cnt)*mn>=ans)//最优性cut 
        return;
    if(cnt==n)
    {
        ans=min(ans,sum);
        return;
    }
    for(int i=1;i<=n;i++)
    {
        if(!vis[i])
        {
            vis[i]=1;
            dfs(i,sum+dist[i][cur],cnt+1);
            vis[i]=0;
        }
    }
}
int main()
{
    while(cin>>n)
    {
        memset(vis,0,sizeof(vis));
        mn=ans=1e7;
        for(int i=1;i<=n;i++)
            cin>>a[i].x>>a[i].y;    
        a[0].x=a[0].y=0;
        for(int i=0;i<=n;i++)
        {
            for(int j=0;j<=n;j++)
            {
                if(i==j) continue;
                dist[i][j]=d(i,j);
                mn=min(mn,dist[i][j]);
            }
        }
        dfs(0,0,0);
        printf("%.2lf\n",ans);
    } 
    
    return 0;    
}