POJ 2031 Building a Space Station G++ 最小生成树 Kruskal实现 prim未实现

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <algorithm>
#include <iomanip>
using namespace std;
//英语     看博友分析     抄博友程序     最小生成树      Kruskal实现     prim未实现 
struct nod{double x;double y;double z;double r;
}da[120];
struct edge{int a;int b;double dis;
};
vector<edge> ve;
bool cmp(edge x, edge y)
{return x.dis<y.dis;
}
double fun(double x1,double y1, double z1,double x2, double y2,double z2)
{return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)+(z1-z2)*(z1-z2));
}
int fa[120];
int find(int x)
{if(fa[x]==-1){return x;}else{return fa[x]=find(fa[x]);}
}
int main()
{while(1){ve.clear();memset(fa,-1,sizeof(fa));int n;cin>>n;	if(n==0){break;}for(int i=0;i<n;i++){cin>>da[i].x>>da[i].y>>da[i].z>>da[i].r;}for(int i=0;i<n;i++){for(int j=i+1;j<n;j++){double t=fun(da[i].x, da[i].y, da[i].z, da[j].x, da[j].y, da[j].z)-da[i].r-da[j].r;if(t<0){t=0;}ve.push_back((edge){i,j,t});}}sort(ve.begin(),ve.end(),cmp);	double ans=0;for(int i=0;i<ve.size();i++){int a=ve[i].a;int b=ve[i].b;if(find(a)!=find(b)){ans=ans+ve[i].dis;fa[find(a)]=find(b);}}cout<<fixed<<setprecision(3)<<ans<<endl; }		return 0;
}