poj 2031 Building a Space Station(最小生成树)

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
struct d
{
    int u,v;
    double w;
} e[10000+5];

bool cmp(d a,d b)
{
    return a.w<b.w;
}

int bin[100+5];
double x[100+5],y[100+5],z[100+5],r[100+5];

int Find(int x)
{
    int s;
    for(s=x; bin[s]>=0; s=bin[s]);

    while(s!=x)
    {
        int t=bin[x];
        bin[x]=s;
        x=t;
    }
    return s;
}

void Union(int x1,int x2)
{
    int f1=Find(x1),f2=Find(x2);
    int t=bin[f1]+bin[f2];
    if(bin[f1]>bin[f2])
    {
        bin[f1]=f2;
        bin[f2]=t;
    }
    else
    {
        bin[f2]=f1;
        bin[f1]=t;
    }

}

int main()
{
    int n,m,i,j,u,v;
    double ans;
    while(~scanf("%d",&n)&&n)
    {
        for(i=0; i<n; i++)
            bin[i]=-1;
        for(i=0; i<n; i++)
            scanf("%lf%lf%lf%lf",&x[i],&y[i],&z[i],&r[i]);

        for(i=0,m=0; i<n; i++)
            for(j=i+1; j<n; j++)
            {
                double t=(x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j])+(z[i]-z[j])*(z[i]-z[j]);
                t=sqrt(t);
                if(t<=r[i]+r[j])
                {
                    if(Find(i)!=Find(j)) Union(i,j);
                }
                else
                {
                    e[m].u=i;
                    e[m].v=j;
                    e[m].w=t-r[i]-r[j];
                    m++;
                }
            }
            sort(e,e+m,cmp);
        for(ans=0,i=0; i<m; i++)
        {
            u=e[i].u;
            v=e[i].v;
            if(Find(u)!=Find(v))
            {
                ans+=e[i].w;
                Union(u,v);
            }
        }
        printf("%.3f
",ans);
    }
    return 0;
}