> 当时为什么没有想着胡搞呢......
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <algorithm>
> #include <time.h>
> #include <math.h>
> using namespace std;
> const int maxn=10001;
> struct point{
>     double a,b,c,d;
> }a[maxn];
> int i,j,k,m,n;
> double best;
> inline double sqr(double s)
> {
>     return s*s;
> }    
> inline double dis(point a1,point a2)
> {
>     return sqrt(sqr(a1.a-a2.a)+sqr(a1.b-a2.b)+sqr(a1.c-a2.c)+sqr(a1.d-a2.d));
> }        
> inline bool cmp(point a1,point a2)
> {
>     return a1.a<a2.a;
> }    
> inline double min(double a1,double a2)
> {
>     return a1<a2?a1:a2;
> }    
> int Random(int st,int ed)
> {
>     return st+rand()%(ed-st+1);
> }    
> int main()
> {
>     while(1)
>     {
>         scanf("%d",&n);
>         if (n==0) return 0;
>         for (i=1;i<=n;i++)
>             scanf("%lf%lf%lf%lf",&a[i].a,&a[i].b,&a[i].c,&a[i].d);
>         best=1000000000;
>         sort(a+1,a+n+1,cmp);
>         for (i=1;i<=n;i++)
>         {
>             int ed=min(i+n/150,n);
>             for (j=i+1;j<=ed;j++)
>             {
>                 best=min(best,dis(a[i],a[j]));
>             }
>             if (ed<n)
>             for (k=1;k<=(n-j)/150+10;k++)
>             {
>                 int s=Random(ed+1,n);
>                 best=min(best,dis(a[i],a[s]));
>             }    
>         }
>         if (best>10000) printf("INFINITY\n");
>         else printf("%.3lf\n",best);    
>     }    
> }