洛谷P1265 公路修建——prim

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#include<cmath>
using namespace std;
const int M=1e5+7;
const double inf=10000007;
int read(){
    int ans=0,f=1,c=getchar();
    while(c<‘0‘||c>‘9‘){if(c==‘-‘) f=-1; c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){ans=ans*10+(c-‘0‘); c=getchar();}
    return ans*f;
}
int n,x[M],y[M],vis[M];
double ans,d[M];
double G_d(int a,int b){return sqrt(1.0*(x[a]-x[b])*(x[a]-x[b])+1.0*(y[a]-y[b])*(y[a]-y[b]));}
void prm(){
    vis[1]=1; d[1]=0.0;
    for(int i=2;i<=n;i++) d[i]=G_d(1,i);
//    for(int i=1;i<=n;i++) printf("%.2lf ",d[i]); puts("");
    for(int i=2;i<=n;i++){
        int id,mn=inf;
        for(int j=2;j<=n;j++)if(!vis[j]&&d[j]<mn) mn=d[j],id=j;
        vis[id]=1;
        for(int j=2;j<=n;j++)if(!vis[j]) d[j]=min(d[j],G_d(id,j));
    }
}
int main(){
    n=read();
    for(int i=1;i<=n;i++) x[i]=read(),y[i]=read();
    prm();
    for(int i=1;i<=n;i++) ans+=d[i];
    printf("%.2lf\n",ans);
    return 0;
}