2019吉林省acm竞赛 G.Spotlight

题意：判断一个点是否一条射线上
思路：先判断这个点是否在这条直线上，然后在射线远处找到一个P点，如果P到这个点的距离小于等于P到起点的距离就在射线上

#include
#include
#include
#include
#include
#include
#define ll long long
using namespace std;
int main() {
	ios::sync_with_stdio(false);
	int t, x, x1, x2, y, y1, y2;
	cin >> t;
	while (t--) {
		cin >> x1 >> y1 >> x2 >> y2 >> x >> y;
		if (x1 == x2 && x1 == x) {
			if (y1 > y2&&y1 >= y || y1 < y2&&y1 <= y)cout << "YES" << endl;
			else cout << "NO" << endl;
			continue;
		}
	//	double a = y2 - y1, b = x1 - x2, c = x2 * y1 - x1 * y2;
		double k = 1.0*(y2 - y1) / (x2 - x1), b = 1.0*(x2*y1 - x1*y2) / (x2 - x1);
		if (y == k * x + b) {
			double tx = 3000.0*x1, ty = 3000.0*(k*x + b);
			double len = sqrt((tx - x)*(tx - x) + (ty - y)*(ty - y));
			double tlen = sqrt((tx - x1)*(tx - x1) + (ty - y1)*(ty - y1));
			if (len <= tlen)cout << "YES" << endl;
			else cout << "NO" << endl;
		}
		else cout << "NO" << endl;
	}
	return 0;
}