我的也是这样的啊，G++ WA，C++ AC，很是奇怪，貌似有浮点数的题目常会有这种问题。
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "math.h"
#define MAXN 105
#define MAXF (1.0e15)
int n,vis[MAXN];
double x[MAXN],y[MAXN],z[MAXN],r[MAXN],d[MAXN][MAXN];

int BuildGraph()
{
    for (int i=0;i<n;i++)
    {
        scanf("%lf%lf%lf%lf",x+i,y+i,z+i,r+i);
    }
    for (int i=0;i<n;i++)
    for (int j=i;j<n;j++)
    {
        if (i==j)
        {
                 d[i][j]=0.0;
        }
        else
        {
            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];
            d[i][j]= dis>0.0?dis:0.0;
            d[j][i]=d[i][j];
        }
    }
    return 0;
}

double Prim()
{
       double sum=0.0,l[MAXN],min;
       int u,i,j;
       memset(vis,0,sizeof(vis));
       u=0;vis[u]=1;
       for (i=0;i<n;i++)
       {
           l[i]=d[u][i];
       }
       for (i=0;i<n;i++)
       {
           min=MAXF;
           for (j=0;j<n;j++)
           {
               if (!vis[j] && l[j]<min)
               {
                           min = l[j];
                           u=j;
               }
           }
           vis[u]=1;
           for (j=0;j<n;j++)
           {
               if   (!vis[j] && l[j]>d[u][j])
               {
                    l[j]=d[u][j];
               }
           }
       }
       for (i=0;i<n;i++)
       sum+=l[i];
       return sum;
}
int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    scanf("%d",&n);
    while (n!=0)
    {
          BuildGraph();
          printf("%.3lf\n",Prim());
       scanf("%d",&n);   
    }
    
    
    return 0;
}