POJ 1269 (直线相交) Intersecting Lines

水题，以前总结的模板还是很好用的。

 1 #include <cstdio>
 2 #include <cmath>
 3 using namespace std;
 4
 5 const double eps = 1e-8;
 6
 7 int dcmp(double x)
 8 {
 9     if(fabs(x) < eps) return 0;
10     return x < 0 ? -1 : 1;
11 }
12
13 struct Point
14 {
15     double x, y;
16     Point(double x=0, double y=0):x(x), y(y) {}
17 };
18 typedef Point Vector;
19
20 Point read_point()
21 {
22     double x, y;
23     scanf("%lf%lf", &x, &y);
24     return Point(x, y);
25 }
26
27 Point operator + (const Point& A, const Point& B)
28 { return Point(A.x+B.x, A.y+B.y); }
29
30 Point operator - (const Point& A, const Point& B)
31 { return Point(A.x-B.x, A.y-B.y); }
32
33 Point operator * (const Point& A, double p)
34 { return Point(A.x*p, A.y*p); }
35
36 double Cross(const Point& A, const Point& B)
37 { return A.x*B.y - A.y*B.x; }
38
39 double Length(const Vector v)
40 { return sqrt(v.x*v.x + v.y*v.y); }
41
42 double DistanceToLine(Point P, Point A, Point B)
43 {
44     Vector v1 = B - A, v2 = P - A;
45     return fabs(Cross(v1, v2)) / Length(v1);
46 }
47
48 Point GetLineIntersection(Point P, Vector v, Point Q, Vector w)
49 {
50     Vector u = P - Q;
51     double t = Cross(w, u) / Cross(v, w);
52     return P + v*t;
53 }
54
55 int main()
56 {
57     //freopen("in.txt", "r", stdin);
58
59     int n;
60     scanf("%d", &n);
61     puts("INTERSECTING LINES OUTPUT");
62     Point A, B, C, D;
63     while(n--)
64     {
65         A = read_point(); B = read_point();
66         C = read_point(); D = read_point();
67         Vector v1 = B - A, v2 = D - C;
68         if(dcmp(Cross(v1, v2)) == 0)
69         {
70             if(dcmp(DistanceToLine(C, A, B)) == 0) puts("LINE");
71             else puts("NONE");
72
73         }
74         else
75         {
76             Point ans = GetLineIntersection(A, v1, C, v2);
77             printf("POINT %.2f %.2f\n", ans.x, ans.y);
78         }
79     }
80     puts("END OF OUTPUT");
81
82     return 0;
83 }

代码君