Line Segment Intersection

#include <bits/stdc++.h>

using namespace std;
using ll = long long;

// Debug printing
#ifdef DEBUG
#define deb(fmt, args...) printf("DEBUG: %d: " fmt, __LINE__, ##args)
#define debug_print(fmt, args...) printf(fmt, ##args)
#else
#define deb(fmt, args...)
#define debug_print(fmt, args...)
#endif

void print_array(vector<int> in, const string title = "Vector")
{
	debug_print("DEBUG: %s [\nDEBUG: ", title.c_str());
	for (unsigned int i = 0; i < in.size(); i++) {
		debug_print("%d ", in[i]);
	}
	debug_print("\nDEBUG: ] END\n");
}

void print_matrix(vector<vector<int> > in, const string title = "Matrix")
{
	debug_print("DEBUG: %s [\nDEBUG: ", title.c_str());
	for (unsigned int i = 0; i < in.size(); i++) {
		for (unsigned int j = 0; j < in[i].size(); j++) {
			debug_print("%d ", in[i][j]);
		}
		debug_print("\nDEBUG: ");
	}
	debug_print("DEBUG: ] END\n");
}

int main(int argc, char *argv[])
{
	ios::sync_with_stdio(0);
	cin.tie(0);

	// Read the input parameters
	int n;
	cin >> n;

	for (int i = 0; i < n; i++) {
		int x1, y1, x2, y2;
		int x3, y3, x4, y4;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;

		// Check if there are shared endpoints.
		if ((x1 == x3 && y1 == y3) || (x1 == x4 && y1 == y4) ||
		    (x2 == x3 && y2 == y3) || (x2 == y4 && x2 == y4)) {
			cout << "YES\n";
			continue;
		}

		// Line segments are on the same line
		int vx1, vy1, vx2, vy2;
		vx1 = x2 - x1;
		vy1 = y2 - y1;
		vx2 = x4 - x3;
		vy2 = y4 - y3;
		int cross = vx1 * vy2 - vx2 * vy1;
		deb("(%d, %d), (%d, %d), cross: %d\n", vx1, vy1, vx2, vy2, cross);
		if (cross == 0 && ((x3 >= x1 && x3 <= x2) || (x4 >= x1 && x4 <= x2)))
		{
			cout << "YES\n";
			continue;
		} else {
			double a, b, k, k2;
			k = 1.0 * (y2 - y1) / (x2 - x1);
			k2 = 1.0 * (y4 - y3) / (x4 - x3);
			a = 1.0 * y3 - k2 * x3;
			b = 1.0 * y1 - k * x1;
			// a = 1.0 * y1 * (x2 - x1) / (y2 - y1);
			// b = 1.0 * y3 * (x4 - x3) / (y4 - y3);
			double x = (a - b) / (k - k2);
			deb("x: %f, a: %f, b: %f, k: %f, k2: %f\n", x, a, b, k, k2);
			if (x >= x1 && x <= x2 && x >= x3 && x <= x4) {
				cout << "YES\n";
				continue;
			}
			// int dx1, dy1, dx2, dy2;
			// dx1 = x3 - x1;
			// dy1 = y3 - y1;
			// dx2 = x3 - x2;
			// dy2 = y3 - y2;
			// int d = abs(dx1 * dy2 - dx2 * dy1) / 2;
			// if ((cross > 0 && d <= 0) || (cross < 0 && d >= 0)) {
			// 	cout << "YES\n";
			// 	continue;
			// }
		}
		cout << "NO\n";
	}
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER