bzoj 1626: [Usaco2007 Dec]Building Roads 修建道路【最小生成树】

先把已有的边并查集了，然后MST即可
记得开double

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
const int N=1005;
int n,m,f[N],con,tot;
double x[N],y[N],ans;
struct qwe
{
    int u,v;
    double w;
}e[N*N];
bool cmp(const qwe &a,const qwe &b)
{
    return a.w<b.w;
}
int read()
{
    int r=0,f=1;
    char p=getchar();
    while(p>'9'||p<'0')
    {
        if(p=='-')
            f=-1;
        p=getchar();
    }
    while(p>='0'&&p<='9')
    {
        r=r*10+p-48;
        p=getchar();
    }
    return r*f;
}
inline int zhao(int x)
{
    return f[x]==x?x:f[x]=zhao(f[x]);
}
int main()
{
    n=read(),m=read();
    for(int i=1;i<=n;i++)
        x[i]=read(),y[i]=read(),f[i]=i;
    for(int i=1;i<=m;i++)
    {
        int x=read(),y=read(),fx=zhao(x),fy=zhao(y);
        if(fx!=fy)
            con++,f[fx]=fy;
    }
    for(int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++)
            if(zhao(i)!=zhao(j))
                e[++tot]=(qwe){i,j,sqrt(abs(x[i]-x[j])*abs(x[i]-x[j])+abs(y[i]-y[j])*abs(y[i]-y[j]))};
    sort(e+1,e+1+tot,cmp);
    for(int i=1;i<=tot&&con<n-1;i++)
    {
        int fu=zhao(e[i].u),fv=zhao(e[i].v);
        if(fu!=fv)
            con++,ans+=e[i].w,f[fu]=fv;
    }
    printf("%.2lf",ans);
    return 0;
}