POJ 1269 (直线相交) Intersecting Lines

水题，以前总结的模板还是很好用的。

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

 const double eps = 1e-;

 int dcmp(double x)
 {
     if(fabs(x) < eps) return ;
     return x <  ? - : ;
 }

 struct Point
 {
     double x, y;
     Point(double x=, double y=):x(x), y(y) {}
 };
 typedef Point Vector;

 Point read_point()
 {
     double x, y;
     scanf("%lf%lf", &x, &y);
     return Point(x, y);
 }

 Point operator + (const Point& A, const Point& B)
 { return Point(A.x+B.x, A.y+B.y); }

 Point operator - (const Point& A, const Point& B)
 { return Point(A.x-B.x, A.y-B.y); }

 Point operator * (const Point& A, double p)
 { return Point(A.x*p, A.y*p); }

 double Cross(const Point& A, const Point& B)
 { return A.x*B.y - A.y*B.x; }

 double Length(const Vector v)
 { return sqrt(v.x*v.x + v.y*v.y); }

 double DistanceToLine(Point P, Point A, Point B)
 {
     Vector v1 = B - A, v2 = P - A;
     return fabs(Cross(v1, v2)) / Length(v1);
 }

 Point GetLineIntersection(Point P, Vector v, Point Q, Vector w)
 {
     Vector u = P - Q;
     double t = Cross(w, u) / Cross(v, w);
     return P + v*t;
 }

 int main()
 {
     //freopen("in.txt", "r", stdin);

     int n;
     scanf("%d", &n);
     puts("INTERSECTING LINES OUTPUT");
     Point A, B, C, D;
     while(n--)
     {
         A = read_point(); B = read_point();
         C = read_point(); D = read_point();
         Vector v1 = B - A, v2 = D - C;
         if(dcmp(Cross(v1, v2)) == )
         {
             if(dcmp(DistanceToLine(C, A, B)) == ) puts("LINE");
             else puts("NONE");

         }
         else
         {
             Point ans = GetLineIntersection(A, v1, C, v2);
             printf("POINT %.2f %.2f\n", ans.x, ans.y);
         }
     }
     puts("END OF OUTPUT");

     return ;
 }

代码君