hdu 4671 异面直线的距离

题目大意：空间中有许多无限长的棒子（圆柱体），求棒子间最小距离。

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <cmath>
 using namespace std;

 const double eps = 1e-;
 struct Point3//三维空间点
 {
     double x, y, z;
     Point3(double x=,double y=,double z=): x(x),y(y),z(z){}
     Point3 operator + (Point3 &t){return Point3(x+t.x, y+t.y, z+t.z);}
     Point3 operator - (Point3 &t) {return Point3(x-t.x, y-t.y, z-t.z);}
     Point3 operator * (double p) {return Point3(x*p, y*p, z*p);}
     Point3 operator / (double p) {return Point3(x/p, y/p, z/p);}
 };
 typedef Point3 Vector3;
 struct Line//空间直线
 {
     Point3 a,b;
 };
 int dcmp(double x)
 {
     if(fabs(x) < eps) return ;
     return x <  ? - : ;
 }
 double Dot(Vector3 A,Vector3 B) { return A.x*B.x + A.y*B.y + A.z*B.z; }
 double Length2(Vector3 A) { return Dot(A, A); }
 Vector3 Cross(Vector3 A, Vector3 B) { return Vector3(A.y*B.z - A.z*B.y, A.z*B.x - A.x*B.z, A.x*B.y - A.y*B.x); }
 inline double min(double a,double b)
 {
     if(dcmp(b-a)>=) return a;
     return b;
 }
 double LineToLine(Line u,Line v)//空间直线间距离
 {
     Vector3 t=Cross(u.a-u.b,v.a-v.b);
     return fabs(Dot(u.a-v.a,t))/sqrt(Length2(t));
 }

 Line L[];
 double R[];

 void init(int i)
 {
     Point3 a,b,c;
     scanf("%lf%lf%lf%lf%lf%lf%lf%lf%lf",&a.x,&a.y,&a.z,&b.x,&b.y,&b.z,&c.x,&c.y,&c.z);
     Vector3 n=Cross(b-a,c-a);//平面法向量
     L[i].a=a;L[i].b=a+n;R[i]=sqrt(Length2(b-a));
 }

 int main()
 {
     int T,i,j,n;
     scanf("%d",&T);
     while(T--)
     {
         scanf("%d",&n);
         for(i=;i<n;i++) init(i);
         bool flag=;
         double ans=1e20;
         for(i=;i<n&&!flag;i++)
         {
             for(j=i+;j<n&&!flag;j++)
             {
                 double temp=LineToLine(L[i],L[j]);
                 if(dcmp(R[i]+R[j]-temp)>=)
                     flag=;
                 else ans=min(ans,temp-R[i]-R[j]);
             }
         }
         if(flag) printf("Lucky\n");
         else printf("%.2lf\n",ans);
     }
     return ;
 }