sortutils.hpp

#include <iostream>
#include <vector>
#include <array>
// this template would tell us the T is not an array like type
// ex. - does not have [n] operator overloaded
// for simplicity - or it's a poorman specialization below

template <typename T>
struct is_arraytype
{
    static const bool value = false;
};

//poorman spec for vector<T>
template <typename T>
struct is_arraytype<std::vector<T>>
{
    static const bool value = true;
};

//poorman spec for array<T>
template <typename T, size_t S>
struct is_arraytype<std::array<T, S>>
{
    static const bool value = true;
};


//a cmp functor
template<typename T>
struct PredCmpT
{
    enum CmpFn
    {
        Lt,
        Gt
    };

    CmpFn m_fn;

    explicit PredCmpT(PredCmpT::CmpFn fn) : m_fn{ fn } { }

    bool operator()(const T& a, const T& b) {
        switch (m_fn)
        {
        case Lt:
            return a < b;
        case Gt:
        default:
            return a > b;
        }
    }
};



//the actual user of the specialization
template<typename T, typename N>
void ssort(T& arr, PredCmpT<N> cmpfn)
{
    //if T is not either std::array or std::vector - don't compile below it.
    if (!is_arraytype<T>::value)
        return;
    int gap, sz;
    sz = arr.size();
    for (gap = sz / 2; gap > 0; gap /= 2)
    {
        for (int i = gap; i < sz; i++)
        {
            for (int j= i - gap; j >=0 && cmpfn(arr[j], arr[j+gap]); j-=gap)
            {
                std::swap(arr[j], arr[j + gap]);
            }
        }
    }
}

//driver tester program 
int main()
{

    std::array<int, 20> arr2 = {1,2,3,4,5,6,7,8,9,8,7,6,5,4,3,2,1};

    std::vector<int> arr = {2,3,4,55,1,1,23,4,50,0,100,200,5,1000,2111,202020,1,0,0,0,
                            8,9,10,11,12,5,6,7,8,9,12345,6789,98765,1234,4321,7890,
                            1919, 2020, 6677, 9988, 1122, 1111, 1212};
    ssort(arr2, PredCmpT<int>{PredCmpT<int>::CmpFn::Gt});
    for(auto it : arr2) {
        std::cout << it << "\r\n";
    }

    return 0;
}