C++, about priority_queue(min max heap)

 vector<int> iV = { 3,5,8,3,6,1,20,4,8,1}; cout << "==========max heap=============" << endl; // building time complexity O(n) priority_queue<int> pq(iV.begin(), iV.end());// default order => max heap, descending order pq.push(24);//O(log n) time complexity while (!pq.empty()) { cout << " " << pq.top() << endl; // --> acces the maximum item : O(1) pq.pop();// O(log n) time complexity } //========== cout << "==========min heap==============" << endl; // min heap, O(n) building time complexity priority_queue<int,vector<int>, std::greater<int>> m_h(iV.begin(),iV.end()); while (!m_h.empty()) { cout << " " << m_h.top() << endl; m_h.pop(); } priority_queue<int, vector<int>, greater<int>> slow_bh; // O(1) building time for (auto i : iV) slow_bh.push(i); // building time O (n* log n)  

struct City { int population; string name; City(int pop = 0, string s = "") { population = pop; name = s; } // for max heap bool operator< (const City& c) const { return population < c.population || (population == c.population && name < c.name); } //for min heap bool operator> (const City& c) const { return population > c.population || (population == c.population && name > c.name); } //bool operator== (const City& c) const / for other methods }; void test_priority_queue() { vector<City> cV = { {100,"suwon"},{320,"incheon"},{40,"seoul"},{500,"kwangju"}}; // max heap cout << "========== max heap =============" << endl; priority_queue<City> pq(cV.begin(), cV.end()); while (!pq.empty()) { cout << " " << pq.top().population << " " << pq.top().name << endl; pq.pop(); } cout << "========== min heap =============" << endl; //min heap priority_queue<City, vector<City>, std::greater<City>> mc_h(cV.begin(), cV.end()); while (!mc_h.empty()) { cout << " " << mc_h.top().population << " " << mc_h.top().name << endl; mc_h.pop(); } }