struct XY {
	size_t x, y;
	XY(size_t x, size_t y) : x(x), y(y) {}
	friend bool operator<(const XY &left_, const XY &right_) {
		if (left_ == right_) return false;
		if (left_.y == right_.y) return left_.x < right_.x;
		return left_.y < right_.y;
	}
	friend bool operator==(const XY &left_, const XY &right_) {
		return left_.x == right_.x;
	}
	friend std::ostream& operator<<(std::ostream &strm, const XY &xy) {
		strm << "[" << xy.x << ":" << xy.y << "]";
		return strm;
	}
};

int main()
{
	std::set<XY> pq;

	pq.emplace(1, 2);
	pq.emplace(1, 3);
	pq.emplace(1, 4);
	pq.emplace(2, 1);
	pq.emplace(3, 4);
	pq.emplace(4, 4);
	pq.emplace(5, 4);
	pq.emplace(6, 4);
	pq.emplace(7, 4);

	for (auto &i : pq) {
		std::cout << i << " ";
	}
	std::cout << std::endl;

	std::set<XY>::iterator i;
	std::cout << std::boolalpha 
		<< (pq.end() != (i = pq.find(XY(1, 0)))) << "\n"
		<< (pq.end() != (i = pq.find(XY(2, 0)))) << "\n"
		<< (pq.end() != (i = pq.find(XY(3, 0)))) << "\n"
		<< (pq.end() != (i = pq.find(XY(4, 0)))) << "\n"
		<< (pq.end() != (i = pq.find(XY(5, 0)))) << "\n"
		<< (pq.end() != (i = pq.find(XY(6, 0)))) << "\n"
		<< (pq.end() != (i = pq.find(XY(7, 0)))) << "\n";

	pq.clear();
	pq.emplace(2, 2);
	pq.emplace(1, 3);

	for (auto &i : pq) {
		std::cout << i << " ";
	}
	std::cout << std::endl;

	std::cout << std::boolalpha 
		<< (pq.end() != (i = pq.find(XY(1, 0)))) << "\n"
		<< (pq.end() != (i = pq.find(XY(2, 0)))) << "\n";
}

[2:1] [1:2] [3:4] [4:4] [5:4] [6:4] [7:4]
false
true   //x == 2 находит, элемент первый в списке
false
false
false
false
false
[2:2] [1:3]
false
true   //x == 2 находит, элемент первый в списке