51onvu - Online IDE & Debugging Tool

#include<bits/stdc++.h>
using namespace std;

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()); }
	// angle to x-axis in interval [-pi, pi]
	double angle() const { return atan2(y, x); }
	double angledegree() const { return atan2(y, x) * 180.0 / acos(-1); }

	P unit() const { return *this/dist(); } // makes dist()=1
	P perp() const { return P(-y, x); } // rotates +90 degrees
	P normal() const { return perp().unit(); }
	// returns point rotated 'a' radians ccw around the origin
	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 << ")"; }
};

void solve(){
    Point<double> a, b; cin >> a.x >> a.y >> b.x >> b.y;
    b = b - a;
    double alpha = b.angledegree();

    int qq; cin >> qq;
    for(int q = 0; q < qq; q++) {
        Point<double> p; cin >> p.x >> p.y;
        p = p - a;
        double beta = p.angledegree();
        beta -= alpha;

        if(abs(0 - beta) < 1e-6){
            double d1 = b.dist2();
            double d2 = p.dist2();
            if(d1 > d2) cout << "ON_SEGMENT\n";
            else cout << "ONLINE_FRONT\n";
        }
        else if(abs(180 - abs(beta)) < 1e-6) cout << "ONLINE_BACK\n";
        else {
            if(beta > 0) cout << "COUNTER_CLOCKWISE\n";
            else cout << "CLOCKWISE\n";
        }
    }
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    cout << fixed << setprecision(8);
    solve();
}