POJ 1269 - Intersecting Lines 直线与直线相交

题意：
    判断直线间位置关系： 相交，平行，重合

 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");
 }