main1.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <cassert>

template <class T,
        class Compare = std::less<typename std::vector <T>::value_type>>
class  priority_queue
{
        typedef typename std::vector<T>::value_type value_type;
        typedef typename std::vector<T>::size_type size_type;
        typedef typename std::vector<T>::reference reference;
        typedef typename std::vector<T>::const_reference const_reference;
    public:
        bool empty() const noexcept { return data.empty(); }
        size_type size() const noexcept { return data.size(); }
        void push(value_type const & value)
        {
            data.push_back(value);
            std::push_heap(std::begin(data), std::end(data), comparer);
        }
        void pop()
        {
            std::pop_heap(std::begin(data), std::end(data), comparer);
            data.pop_back();
        }
        const_reference top() const { return data.front(); }
        void swap(priority_queue& other) noexcept
        {
            swap(data, other.data);
            swap(comparer, other.comparer);
        }
    private:
        std::vector<T> data;
        Compare comparer;
};

template<class T, class Compare>
    void swap(priority_queue<T, Compare>& lhs,
            priority_queue<T, Compare>& rhs)
    noexcept(noexcept(lhs.swap(rhs)))
    {
        lhs.swap(rhs);
    }
//This class can be used as follows:
int main()
{
    priority_queue<int> q;
    for (int i : {1, 5, 3, 1, 13, 21, 8})
    {
        q.push(i);
    }
    assert(!q.empty());
    assert(q.size() == 7);
    while (!q.empty())
    {
        std::cout << q.top() << ' ';
        q.pop();
    }
}