C - Building a Space Station

#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define MAXN 1001
using namespace std;
int n,m;
int fa[MAXN];
long double ans;
struct nond{
    long double x,y,z,r;
}v[MAXN];
 
struct none{
    int x,y;long double z;
}edge[10010];
int cmp(none a,none b){
    return a.z<b.z;
}
int find(int x){
    if(fa[x]==x)    return x;
    else return fa[x]=find(fa[x]);
}
int main(){
    while(scanf("%d",&n)&&n){
        for(int i=1;i<=n;i++)
            cin>>v[i].x>>v[i].y>>v[i].z>>v[i].r;
        
 
for(int i=1;i<=n;i++){
            for(int j=i+1;j<=n;j++){
                long double tmp=sqrt((v[i].x-v[j].x)*(v[i].x-v[j].x)+(v[i].y-v[j].y)*(v[i].y-v[j].y)+(v[i].z-v[j].z)*(v[i].z-v[j].z));
                tmp-=v[i].r;tmp-=v[j].r;
                if(tmp<=0){ edge[++m].x=i;edge[m].y=j;edge[m].z=0.0
 
; }
                else { edge[++m].x=i;edge[m].y=j;edge[m].z=tmp; }
            }
        }
        for(int i=1;i<=n;i++)    fa[i]=i;
        sort(edge+1,edge+1+m,cmp);
        for(int i=1;i<=m;i++){
            int dx=find(edge[i].x);
            int dy=find(edge[i].y);
            if(dx==dy)    continue;
            fa[dy]=dx;
            ans+=edge[i].z;
        }
        double bns=double(ans);
        printf("%.3lf\n",bns);ans=0;m=0;
    }
}

POJ 2031 Building a Space Station