P2872 [USACO07DEC] Building Roads S

点击查看代码

#include<bits/stdc++.h>
using namespace std;

const int N=1010,M=1000*500+50;
int n,m;
int x[N],y[N];
struct Edge{
    int a,b;
    double w;
    bool operator<(const Edge& W) const{
        return w<W.w;
    }
}edges[M];
int p[N];
int find(int x)
{
    if(p[x]!=x) p[x]=find(p[x]);
    return p[x];
}

double get_dist(int i,int j)
{
    double dx=x[i]-x[j],dy=y[i]-y[j];
    return sqrt(dx * dx + dy * dy);
}

int main()
{
    ios::sync_with_stdio(0),cin.tie(0);
    cin>>n>>m;
    for(int i=1;i<=n;i++){
        cin>>x[i]>>y[i];
    }

    for(int i=1;i<=m;i++){
        cin>>edges[i].a>>edges[i].b;
    }

    for(int i=1;i<=n;i++) p[i]=i;


    int cnt=0;
    for(int i=1;i<=m;i++){
        int a=find(edges[i].a),b=find(edges[i].b);
        double w=edges[i].w;
        if(a!=b){
            p[a]=b;
            cnt++;
        }
    }

    int edge_cnt=0;
    for(int i=1;i<=n;i++){
        for(int j=i+1;j<=n;j++){
            edges[++edge_cnt]={i,j,get_dist(i,j)};
        }
    }
    
    sort(edges+1, edges+edge_cnt+1);

    double res=0;
    for(int i=1;i<=edge_cnt;i++){
        int a=find(edges[i].a),b=find(edges[i].b);
        double w=edges[i].w;
        if(a!=b){
            p[a]=b;
            res+=w;
            if(++cnt==n-1){break;}
        }
    }

    cout<<fixed<<setprecision(2)<<res<<"\n";

    return 0;

    

    
}