P1265 公路修建

裸prim

//P1265 公路修建
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int inf=987654321;
struct cc{
    ll x,y;
}a[5005];
bool v[5005];
double d[5005];
inline int read(){
    int k=0,f=1;
    char c=getchar();
    while(!isdigit(c)){
        if(c=='-') f=-1;
        c=getchar(); 
    }
    while(isdigit(c)){
        k=(k<<1)+(k<<3)+(c^48);
        c=getchar();
    }
    return k*f;
}
inline double cal(int x,int y){
    return sqrt((double)(a[x].x-a[y].x)*(a[x].x-a[y].x)+(double)(a[x].y-a[y].y)*(a[x].y-a[y].y));
}
int main(){
    int n;
    n=read();
    for(int i=1;i<=n;i++){
        a[i].x=read();
        a[i].y=read();
        d[i]=inf;
    }
    int pos;
    d[1]=0;
    double ans=0;
    for(int i=1;i<=n;i++){
        double minn=inf;
        for(int j=1;j<=n;j++){
            if(!v[j]&&d[j]<minn){
                minn=d[j];
                pos=j;
            } 
        }
        ans+=minn;v[pos]=1;
        for(int j=1;j<=n;j++){
            double dd=cal(pos,j); //边计算边修改 
            if(d[j]>dd) d[j]=dd; 
        }
    }
    printf("%.2lf",ans);
    return 0;
}