Line Segment Intersection

#include <iostream>
#include <ccomplex>
#include <vector>

using namespace std;

typedef long long C;
typedef complex<C> P;
#define X real()
#define Y imag()
#define cross(a,b) (conj(a)*(b)).Y

int orientation(P p, P q, P r) {
    C val = cross(q - p, r - q);
    if (val == 0) return 0;
    return (val > 0) ? 1 : 2;
}

bool onSegment(P p, P q, P r) {
    return min(p.X, r.X) <= q.X && q.X <= max(p.X, r.X) &&
           min(p.Y, r.Y) <= q.Y && q.Y <= max(p.Y, r.Y);
}

bool intersection(P p1, P q1, P p2, P q2) {
    int o1 = orientation(p1, q1, p2);
    int o2 = orientation(p1, q1, q2);
    int o3 = orientation(p2, q2, p1);
    int o4 = orientation(p2, q2, q1);

    if (o1 != o2 && o3 != o4) return true;

    if (o1 == 0 && onSegment(p1, p2, q1)) return true;
    if (o2 == 0 && onSegment(p1, q2, q1)) return true;
    if (o3 == 0 && onSegment(p2, p1, q2)) return true;
    if (o4 == 0 && onSegment(p2, q1, q2)) return true;

    return false;
}

int main() {
    int t;
    cin >> t;
    for (int i = 0; i < t; i++) {
        vector<P> vec(4);
        
        for (int l = 0; l < 4; l++) {
            C a, b;
            cin >> a >> b;
            vec[l] = {a, b};
        }

        if (intersection(vec[0], vec[1], vec[2], vec[3])) {
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED