luogu_1265 公路修建

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
const int N=5010;
const int INF=1<<30;
int n,x[N],y[N],vis[N];
double ans,d[N];

double dist(int a,int b){
	double dx=abs(x[a]-x[b]),dy=abs(y[a]-y[b]);
	return sqrt(dx*dx+dy*dy);
}

int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++)scanf("%d%d",&x[i],&y[i]);
	for(int i=2;i<=n;i++)d[i]=dist(1,i);
	vis[1]=1;
	for(int i=2;i<=n;i++){
		int v=-1;
		double minn=INF;
		for(int j=1;j<=n;j++)
			if(!vis[j] && d[j]<minn){
				minn=d[j];
				v=j;
			}
		vis[v]=1;
		ans+=minn;
		for(int j=1;j<=n;j++)
			if(!vis[j]){
				double d1=dist(v,j);
				d[j]=min(d[j],d1);
		}
	}
	printf("%.2lf
",ans);
	return 0;
}