萌新求助

struct stu1 {
	int x, y;
	bool operator < (const stu1 &p) const {
		return this -> x < p.x;
	}
};

struct stu2 {
	int x, y;
	friend bool operator < (const stu2 &p, const stu2 &q) {
		return p.x < q.x;
	}
};