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-8;

int dcmp(double x)
{
    if(fabs(x) < eps) return 0;
    return x < 0 ? -1 : 1;
}

struct Point
{
    double x, y;
    Point(double x=0, double y=0):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)) == 0)
        {
            if(dcmp(DistanceToLine(C, A, B)) == 0) puts("LINE");
            else puts("NONE");

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

    return 0;
}