#include <iostream>
#include <queue>
#include <vector>
#include <functional>     // for greater<int>
#include <string>
using namespace std;

// "Non-destructive" print function?
template<typename T> void print_queue(T q)
{
    while(!q.empty())
    {
        std::cout << q.top() << " ";
        q.pop();
    }
    std::cout << '\n';
}

// a binary predicate (function object/functor) for comparing two strings
// returns true if first string is shorter than second string
struct longer
{
    bool operator()(const string& a, const string& b)
    {
        return a.size() < b.size();
    }
};

int main ()
{
    int myints[]= {10,60,50,20};
    vector<int> v1{10,20,30,40};
    vector<string> v2{"Have","a","really","very","nice","day","."};

    // pq1, pq2, pq3 uses default < comparison for type int
    priority_queue<int> pq1;
    priority_queue<int> pq2 (v1.begin(), v1.end());
    priority_queue<int> pq3 (myints,myints+4);

    // pq4 uses default > comparison for type int to determine priority
    priority_queue<int, vector<int>, std::greater<int> > pq4 (myints,myints+4);

    // pq5 uses default < comparison for type string
    priority_queue<string> pq5 (v2.begin(),v2.end());

    // pq6 uses longer binary predicate comparison for type string to determine priority
    priority_queue<string, vector<string>, longer> pq6 (v2.begin(),v2.end());

    cout << "pq2 = ";    print_queue(pq2);
    cout << "pq3 = ";    print_queue(pq3);
    cout << "pq4 = ";    print_queue(pq4);
    cout << "pq5 = ";    print_queue(pq5);
    cout << "pq6 = ";    print_queue(pq6);

    cout << "pq3.size()=" << pq3.size() << endl;
    cout << "pq4.size()=" << pq4.size() << endl << endl;

    cout << "pq2 and pq3 swapped" << endl;
    pq2.swap(pq3);
    //  pq3.swap(pq4);  ERROR - why?
    cout << "pq2 = ";    print_queue(pq2);

    pq2.push(95);
    pq2.push(5);
    pq2.push(25);
    pq2.emplace(35);
    cout << "pq2 = ";    print_queue(pq2);
}