Line Intersection.cpp

template <class T>
int sgn(T x)
{
	return (x > 0) - (x < 0);
}
template <class T>
struct Point
{
	typedef Point P;
	T x, y;
	explicit Point(T x = 0, T y = 0) : x(x), y(y) {}
	bool operator<(P p) const { return tie(x, y) < tie(p.x, p.y); }
	bool operator==(P p) const { return tie(x, y) == tie(p.x, p.y); }
	P operator+(P p) const { return P(x + p.x, y + p.y); }
	P operator-(P p) const { return P(x - p.x, y - p.y); }
	P operator*(T d) const { return P(x * d, y * d); }
	P operator/(T d) const { return P(x / d, y / d); }
	T dot(P p) const { return x * p.x + y * p.y; }
	T cross(P p) const { return x * p.y - y * p.x; }
	T cross(P a, P b) const { return (a - *this).cross(b - *this); }
	T dist2() const { return x * x + y * y; }
	double dist() const { return sqrt((double)dist2()); }
	double angle() const { return atan2(y, x); }
	P unit() const { return *this / dist(); }
	P perp() const { return P(-y, x); }
	P normal() const { return perp().unit(); }
	P rotate(double a) const { return P(x * cos(a) - y * sin(a), x * sin(a) + y * cos(a)); }
	friend ostream &operator<<(ostream &os, P p) { return os << "(" << p.x << "," << p.y << ")"; }
};
template <class P>
pair<int, P> lineInter(P s1, P e1, P s2, P e2)
{
	auto d = (e1 - s1).cross(e2 - s2);
	if (d == 0) 
		return {-(s1.cross(e1, s2) == 0), P(0, 0)};
	auto p = s2.cross(e1, e2), q = s2.cross(e2, s1);
	return {1, (s1 * p + e1 * q) / d};
}
//Use:  auto res=lineInter(s1,e1,s2,e2);
 //if(res.first==1)
 //cout<<"intersectionpointat"<<res.second<<endl;