CombinedPermutationGenerator.hpp

#pragma once
#include <samchon/library/CaseGenerator.hpp>

namespace samchon
{
namespace library
{
    class CombinedPermutationGenerator
        : public CaseGenerator
    {
    private:
        typedef CaseGenerator super;

        std::vector<size_t> dividers;

    public:
        CombinedPermutationGenerator(size_t n, size_t r)
            : super(n, r)
        {
            this->size_ = (size_t)pow(n, r);

            dividers.assign(r, 0);
            for (size_t i = 0; i < r; i++)
            {
                size_t x = r - (i + 1);
                dividers[i] = (size_t)pow(n, x);
            }
        };
        virtual ~CombinedPermutationGenerator() = default;

        virtual auto operator[](size_t index) const->std::vector<size_t> override
        {
            std::vector<size_t> row(r_, 0);
            
            for (size_t i = 0; i < row.size(); i++)
                row[i] = (index / dividers[i]) % n_;

            return row;
        };
    };
};
};