Building a Space Station——最小生成树

#include<iostream>
#include<stdio.h>
#include<math.h>
#include<algorithm>
#include<cstring>
#include<vector>
#define eps 1e-8
using namespace std;
typedef long long ll;
const int maxn = 1e6+5;
int f[maxn];
int cnt,n;
double x[maxn],y[maxn],z[maxn],r[maxn];
struct node
{
    int u,v;
    double w;
    bool operator < (const node &a)const
    {
        return w<a.w;
    }
}edge[maxn];
int sign(double x)
{
    if(fabs(x)<eps)return 0;
    return x<0?-1:1;
}
int Find(int x)
{
    return x==f[x]?x:f[x]=Find(f[x]);
}
double kruskal()
{
    double ans=0.0;
    for(int i=0; i<=n; i++)f[i]=i;
    sort(edge,edge+cnt);
    for(int i=0; i<cnt; i++)
    {
        int x=edge[i].u;
        int y=edge[i].v;
        int fx=Find(x);
        int fy=Find(y);
        if(fx!=fy)
        {
            f[fx]=fy;
            ans+=edge[i].w;
        }
    }
    return ans;

}
double get_dis(int i,int j)
{
    double dis=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j])+(z[i]-z[j])*(z[i]-z[j]))-(r[i]+r[j]);
    if(dis>=0)return dis;
    return 0;
}
int main()
{
    while(~scanf("%d",&n) && n)
    {
        memset(edge,0,sizeof edge);
        for(int i=1; i<=n; i++)scanf("%lf%lf%lf%lf",&x[i],&y[i],&z[i],&r[i]);

        cnt=0;
        for(int i=1; i<=n; i++)
        {
            for(int j=i+1; j<=n; j++)
            {
                edge[cnt].u=i;
                edge[cnt].v=j;
                edge[cnt++].w=get_dis(i,j);
            }
        }
        printf("%.3f\n",kruskal());

    }
    return 0;
}