// 最小生成树 Kruskal算法 O(MlogM)
#include<bits/stdc++.h>
using namespace std;

const int N=1010,M=1000010;
int n,m,tot,cnt,x[N],y[N],fa[N];
double ans;
pair<double,pair<int,int> >e[M]; //边集

int find(int u){ //并查集的找根
  return fa[u]==u?u:fa[u]=find(fa[u]);
}
void kruskal(){
  for(int i=1;i<=n;i++) fa[i]=i;
  sort(e+1,e+cnt+1); //排序
  for(int i=1; i<=cnt; i++){
    int x=find(e[i].second.first),y=find(e[i].second.second);
    if(x!=y){
      fa[x]=y;
      ans+=e[i].first;
      if(++tot==n-1) break;
    }
  }
  printf("%.2lf\n",ans);
}
int main(){
  cin>>n>>m;
  for(int i=1;i<=n;i++){
    scanf("%d %d",&x[i],&y[i]);
    for(int j=1;j<i;j++){
      double d=sqrt((double)(x[i]-x[j])*(x[i]-x[j])+(double)(y[i]-y[j])*(y[i]-y[j]));
      e[++cnt]={d,{i,j}};
    }
  }
  for(int i=1,u,v; i<=m; i++){
    scanf("%d %d",&u,&v);
    e[++cnt]={0.0,{u,v}}; //m条边必选
  }
    
  kruskal();
}

#include<bits/stdc++.h>
using namespace std;
const int N=1010;
#define PII pair<double,double>
#define fi first
#define se second
PII a[N];
double dis(PII n1,PII n2){return sqrt((n1.fi-n2.fi)*(n1.fi-n2.fi)+(n1.se-n2.se)*(n1.se-n2.se));}
struct node{int x,y;double c;}e[N*N];
bool cmp(node n1,node n2){return n1.c<n2.c;}
int fa[N];
int findfa(int x){return fa[x]==x?fa[x]:fa[x]=findfa(fa[x]);}
int main()
{
    int n,m;cin>>n>>m;
    for(int i=1;i<=n;i++)cin>>a[i].fi>>a[i].se;
    int len=0;
    for(int i=1;i<=n;i++)for(int j=i+1;j<=n;j++)e[++len]={i,j,dis(a[i],a[j])};
    for(int i=1;i<=n;i++)fa[i]=i;
    for(int i=1;i<=m;i++)
    {
        int x,y;cin>>x>>y;
        int tx=findfa(x),ty=findfa(y);
        fa[tx]=ty;
    }
    sort(e+1,e+len+1,cmp);
    int sum=m;double ans=0;
    for(int i=1;i<=len;i++)
    {
        int tx=findfa(e[i].x),ty=findfa(e[i].y);
        if(tx!=ty)
        {
            fa[tx]=ty;
            sum++;ans+=e[i].c;
            if(sum==n-1)break;
        }
    }
    printf("%.2lf",ans);
    return 0;
}

qkw代码：

#include<bits/stdc++.h>
using namespace std;
const int N=1010;
#define PII pair<double,double>
#define fi first
#define se second
PII a[N];
double dis(PII n1,PII n2){return sqrt((n1.fi-n2.fi)*(n1.fi-n2.fi)+(n1.se-n2.se)*(n1.se-n2.se));}
struct node{int x,y;double c;}e[N*N];
bool cmp(node n1,node n2){return n1.c<n2.c;}
int fa[N];
int findfa(int x){return fa[x]==x?fa[x]:fa[x]=findfa(fa[x]);}
int main()
{
    int n,m;cin>>n>>m;
    for(int i=1;i<=n;i++)cin>>a[i].fi>>a[i].se;
    int len=0;
    for(int i=1;i<=n;i++)for(int j=i+1;j<=n;j++)e[++len]={i,j,dis(a[i],a[j])};
    for(int i=1;i<=n;i++)fa[i]=i;
    for(int i=1;i<=m;i++)
    {
        int x,y;cin>>x>>y;
        int tx=findfa(x),ty=findfa(y);
        fa[tx]=ty;
    }
    sort(e+1,e+len+1,cmp);
    int sum=m;double ans=0;
    for(int i=1;i<=len;i++)
    {
        int tx=findfa(e[i].x),ty=findfa(e[i].y);
        if(tx!=ty)
        {
            fa[tx]=ty;
            sum++;ans+=e[i].c;
            if(sum==n-1)break;
        }
    }
    printf("%.2lf",ans);
    return 0;
}