#include <iterator>

    struct RandomIterator
    {
        using iterator_category = std::bidirectional_iterator_tag;
        using difference_type   = std::ptrdiff_t;
        using value_type        = int;
        using pointer           = value_type *;
        using reference         = value_type &;

        private:
            int d_value;

        public:
            RandomIterator(int init);

// standard:
            bool operator==(RandomIterator const &other) const;
            bool operator!=(RandomIterator const &other) const;
            int &operator*();
            RandomIterator &operator++();

// required:
            int operator-(RandomIterator const &rhs) const;
            RandomIterator operator+(int step) const;
            RandomIterator operator-(int step) const;
            bool operator<(RandomIterator const &other) const;

// consider:
            int *operator->() const;
            RandomIterator &operator--();
            RandomIterator operator--(int);
            RandomIterator operator++(int);
            RandomIterator &operator-=(int step);
            RandomIterator &operator+=(int step);
    };

RandomIterator::RandomIterator(int init)
:
    d_value(init)
{}

bool RandomIterator::operator!=(RandomIterator const &other) const
{
    return d_value != other.d_value;
}

bool RandomIterator::operator==(RandomIterator const &other) const
{
    return d_value == other.d_value;
}

bool RandomIterator::operator<(RandomIterator const &other) const
{
    return d_value < other.d_value;
}

int RandomIterator::operator-(RandomIterator const &rhs) const
{
    return 0;
}

RandomIterator RandomIterator::operator+(int step) const
{
    return *this;
}

RandomIterator RandomIterator::operator-(int step) const
{
    return *this;
}

RandomIterator &RandomIterator::operator--()
{
    return *this;
}

RandomIterator &RandomIterator::operator++()
{
    return *this;
}

int &RandomIterator::operator*()
{
    return d_value;
}