今天的比赛前面四个多小时没有出题，智商真是拙计；
其实前面都是水题，就是想不到思路！
知道最后40分钟，和小珺同志把这个计算几何的题给A了；
然后小琪也马上把第3题干掉了；
代码：
1 #include<cstdio> 2 #include<cstring> 3 #include<cmath> 4 using namespace std; 5 struct point3 6 { 7 double x,y,z; 8 }; 9 10 //向量大小 11 double vlen(point3 p) 12 { 13 return sqrt(p.x*p.x+p.y*p.y+p.z*p.z); 14 } 15 16 //计算 dot product U . V 17 double dmult(point3 u,point3 v) 18 { 19 return u.x*v.x+u.y*v.y+u.z*v.z; 20 } 21 22 //计算 cross product U x V 23 point3 xmult(point3 u,point3 v) 24 { 25 point3 ret; 26 ret.x=u.y*v.z-v.y*u.z; 27 ret.y=u.z*v.x-u.x*v.z; 28 ret.z=u.x*v.y-u.y*v.x; 29 return ret; 30 } 31 //矢量差 U - V 32 point3 subt(point3 u,point3 v) 33 { 34 point3 ret; 35 ret.x=u.x-v.x; 36 ret.y=u.y-v.y; 37 ret.z=u.z-v.z; 38 return ret; 39 } 40 41 point3 intersection(point3 u1,point3 u2,point3 v1,point3 v2) 42 { 43 point3 ret=u1; 44 double t=((u1.x-v1.x)*(v1.y-v2.y)-(u1.y-v1.y)*(v1.x-v2.x)) 45 /((u1.x-u2.x)*(v1.y-v2.y)-(u1.y-u2.y)*(v1.x-v2.x)); 46 ret.x+=(u2.x-u1.x)*t; 47 ret.y+=(u2.y-u1.y)*t; 48 ret.z+=(u2.z-u1.z)*t; 49 printf("%0.6lf %0.6lf %0.6lf ",ret.x,ret.y,ret.z); 50 return ret; 51 } 52 53 double linetoline(point3 u1,point3 u2,point3 v1,point3 v2) 54 { 55 point3 a=subt(u1,u2); 56 point3 b=subt(v1,v2); 57 58 //point3 ans=intersection(u1,u2,a,b); 59 point3 n=xmult(a,b); 60 return fabs(dmult(subt(u1,v1),n))/vlen(n); 61 } 62 63 point3 add(point3 a,point3 b) 64 { 65 point3 ret; 66 ret.x=a.x+b.x; 67 ret.y=a.y+b.y; 68 ret.z=a.z+b.z; 69 return ret; 70 } 71 72 int main() 73 { 74 point3 a,b,c,d; 75 int t; 76 scanf("%d",&t); 77 while(t--) 78 { 79 scanf("%lf%lf%lf",&a.x,&a.y,&a.z); 80 scanf("%lf%lf%lf",&b.x,&b.y,&b.z); 81 scanf("%lf%lf%lf",&c.x,&c.y,&c.z); 82 scanf("%lf%lf%lf",&d.x,&d.y,&d.z); 83 printf("%.6lf ",linetoline(a,b,c,d)); 84 point3 x1=subt(a,b); 85 point3 x2=subt(c,d); 86 point3 n=xmult(x1,x2); 87 double k=d.x-c.x;//kk:k k:K 88 double l=d.y-c.y; 89 double m=d.z-c.z; 90 double h=b.x-a.x; 91 double i=b.y-a.y; 92 double j=b.z-a.z; 93 double N=h*i*l-i*i*k-j*j*k+h*j*m; 94 double O=h*h*l-h*i*k-i*j*m+j*j*l; 95 double P=h*j*k-h*h*m-i*i*m+i*j*l; 96 double Q=-a.x*N+a.y*O-a.z*P; 97 double kk=(O*c.y-N*c.x-P*c.z-Q)/(N*k-O*l+P*m); 98 point3 ss; 99 ss.x=k*kk+c.x; 100 ss.y=l*kk+c.y; 101 ss.z=m*kk+c.z; 102 point3 ans=intersection(ss,add(ss,n),a,b); 103 printf("%.6lf %.6lf %.6lf ",k*kk+c.x,l*kk+c.y,m*kk+c.z); 104 } 105 return 0; 106 }