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-8;
struct Point3//三维空间点
{
    double x, y, z;
    Point3(double x=0,double y=0,double z=0): 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 0;
    return x < 0 ? -1 : 1;
}
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)>=0) 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[35];
double R[35];

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=0;i<n;i++) init(i);
        bool flag=0;
        double ans=1e20;
        for(i=0;i<n&&!flag;i++)
        {
            for(j=i+1;j<n&&!flag;j++)
            {
                double temp=LineToLine(L[i],L[j]);
                if(dcmp(R[i]+R[j]-temp)>=0)
                    flag=1;
                else ans=min(ans,temp-R[i]-R[j]);
            }
        }
        if(flag) printf("Lucky
");
        else printf("%.2lf
",ans);
    }
    return 0;
}