hdu 4671 异面直线的距离

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cmath>
 5 using namespace std;
 6 
 7 const double eps = 1e-8;
 8 struct Point3//三维空间点
 9 {
10     double x, y, z;
11     Point3(double x=0,double y=0,double z=0): x(x),y(y),z(z){}
12     Point3 operator + (Point3 &t){return Point3(x+t.x, y+t.y, z+t.z);}
13     Point3 operator - (Point3 &t) {return Point3(x-t.x, y-t.y, z-t.z);}
14     Point3 operator * (double p) {return Point3(x*p, y*p, z*p);}
15     Point3 operator / (double p) {return Point3(x/p, y/p, z/p);}
16 };
17 typedef Point3 Vector3;
18 struct Line//空间直线
19 {
20     Point3 a,b;
21 };
22 int dcmp(double x)
23 {
24     if(fabs(x) < eps) return 0;
25     return x < 0 ? -1 : 1;
26 }
27 double Dot(Vector3 A,Vector3 B) { return A.x*B.x + A.y*B.y + A.z*B.z; }
28 double Length2(Vector3 A) { return Dot(A, A); }
29 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); }
30 inline double min(double a,double b)
31 {
32     if(dcmp(b-a)>=0) return a;
33     return b;
34 }
35 double LineToLine(Line u,Line v)//空间直线间距离
36 {
37     Vector3 t=Cross(u.a-u.b,v.a-v.b);
38     return fabs(Dot(u.a-v.a,t))/sqrt(Length2(t));
39 }
40 
41 Line L[35];
42 double R[35];
43 
44 void init(int i)
45 {
46     Point3 a,b,c;
47     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);
48     Vector3 n=Cross(b-a,c-a);//平面法向量
49     L[i].a=a;L[i].b=a+n;R[i]=sqrt(Length2(b-a));
50 }
51 
52 int main()
53 {
54     int T,i,j,n;
55     scanf("%d",&T);
56     while(T--)
57     {
58         scanf("%d",&n);
59         for(i=0;i<n;i++) init(i);
60         bool flag=0;
61         double ans=1e20;
62         for(i=0;i<n&&!flag;i++)
63         {
64             for(j=i+1;j<n&&!flag;j++)
65             {
66                 double temp=LineToLine(L[i],L[j]);
67                 if(dcmp(R[i]+R[j]-temp)>=0)
68                     flag=1;
69                 else ans=min(ans,temp-R[i]-R[j]);
70             }
71         }
72         if(flag) printf("Lucky\n");
73         else printf("%.2lf\n",ans);
74     }
75     return 0;
76 }