POJ 1269 - Intersecting Lines 直线与直线相交

 include <iostream>

 #include <cstdio>

 using namespace std;

 struct Point

 {

     int x , y;

     Point(int a = , int b = ) :x(a), y(b) {}

 };

 struct Line

 {

     Point s, e;

     int a, b, c;//a>=0

     Line() {}

     Line(Point s1,Point e1) : s(s1), e(e1) {}

     void Coefficient()//get a,b,c

     {

         a = e.y - s.y;

         b = s.x - e.x;

         c = e.x * s.y - s.x * e.y;

         if(a < ) a = -a,b = -b,c = -c;

     }

 };

 int Line_Inter_Line(Line & l1,Line & l2, double &x,double &y)//直线 平行: 0, 相交：1, 重合: 2

 {

     l1.Coefficient();

     l2.Coefficient();

     if(l1.a * l2.b == l2.a * l1.b)

     {

         if(l1.b * l2.c != l1.c * l2.b || l1.a * l2.c != l1.c * l2.a) return ;

         else return ;

     }

     x =(double) - (l1.c * l2.b - l2.c * l1.b) / (l1.a * l2.b - l2.a * l1.b);// (c1b2-c2b1)/(a1b2-a2b1)

     y =(double)   (l1.c * l2.a - l2.c * l1.a) / (l1.a * l2.b - l2.a * l1.b);// (c1a2-c2a1)/(a1b2-a2b1)

     return ;

 }

 int n;

 int main()

 {

     puts("INTERSECTING LINES OUTPUT");

     scanf("%d", &n);

     while (n--)

     {

         Point p1, p2, p3, p4;

         double x, y;

         scanf("%d%d%d%d%d%d%d%d",&p1.x, &p1.y, &p2.x, &p2.y, &p3.x, &p3.y, &p4.x, &p4.y);

         Line l1 = Line(p1, p2), l2 = Line(p3, p4);

         int f = Line_Inter_Line(l1, l2, x, y);

         if (f == ) puts("NONE");

         else if (f == ) puts("LINE");

         else printf("POINT %.2f %.2f\n", x, y);

     }

     puts("END OF OUTPUT");

 }