#include <iostream>#include <queue>#include <functional>using namespace std;int main() {    priority_queue<int> pq1; // plus vector<int> and less<int>    priority_queue<int,vector<int>,greater<int> > pq2;    pq1.push(3); pq1.push(1); pq1.push(2);    pq2.push(3); pq2.push(1); pq2.push(2);    int a[] = {4,6,5};    priority_queue<int> pq3(a,a+3);    while (!pq1.empty()) {         cout << pq1.top() << ' ';    // 3 2 1        pq1.pop();    }    while (!pq2.empty()) {         cout << pq2.top() << ' ';    // 1 2 3        pq2.pop();    }    while (!pq3.empty()) {         cout << pq3.top() << ' ';    // 6 5 4        pq3.pop();    }    return 0;}