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

 1 include <iostream>
 2 #include <cstdio>
 3 using namespace std;
 4 struct Point
 5 {
 6     int x , y;
 7     Point(int a = 0, int b = 0) :x(a), y(b) {}
 8 };
 9 struct Line
10 {
11     Point s, e;
12     int a, b, c;//a>=0
13     Line() {}
14     Line(Point s1,Point e1) : s(s1), e(e1) {}
15     void Coefficient()//get a,b,c
16     {
17         a = e.y - s.y;
18         b = s.x - e.x;
19         c = e.x * s.y - s.x * e.y;
20         if(a < 0) a = -a,b = -b,c = -c;
21     }
22 };
23 int Line_Inter_Line(Line & l1,Line & l2, double &x,double &y)//直线 平行: 0, 相交：1, 重合: 2
24 {
25     l1.Coefficient();
26     l2.Coefficient();
27     if(l1.a * l2.b == l2.a * l1.b)
28     {
29         if(l1.b * l2.c != l1.c * l2.b || l1.a * l2.c != l1.c * l2.a) return 0;
30         else return 2;
31     }
32     x =(double) - (l1.c * l2.b - l2.c * l1.b) / (l1.a * l2.b - l2.a * l1.b);// (c1b2-c2b1)/(a1b2-a2b1)
33     y =(double)   (l1.c * l2.a - l2.c * l1.a) / (l1.a * l2.b - l2.a * l1.b);// (c1a2-c2a1)/(a1b2-a2b1)
34     return 1;
35 }
36 int n;
37 int main()
38 {
39     puts("INTERSECTING LINES OUTPUT");
40     scanf("%d", &n);
41     while (n--)
42     {
43         Point p1, p2, p3, p4;
44         double x, y;
45         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);
46         Line l1 = Line(p1, p2), l2 = Line(p3, p4);
47         int f = Line_Inter_Line(l1, l2, x, y);
48         if (f == 0) puts("NONE");
49         else if (f == 2) puts("LINE");
50         else printf("POINT %.2f %.2f\n", x, y);
51     }
52     puts("END OF OUTPUT");
53 }