#include <cstdint>
#include <iterator>
#include <vector>

namespace mystd
{

using It = std::vector<std::int32_t>::iterator;
using DifferenceType = It::difference_type;

/* advence: advances iterator it by n steps */
void advance(It &it, DifferenceType n)
{
    it += n;
}

/* distance: returns number of steps needed to go from first to last */
DifferenceType distance(It first, It last)
{
    auto dist = DifferenceType{0};

    for (; first < last; ++dist)
        ++first;
    for (; first > last; --dist)
        --first;

    return dist;
}

/* next: returns next iterator */
It next(It it, DifferenceType n = 1)
{
    return it + n;
}

/* prev: returns previous iterator */
It prev(It it, DifferenceType n = 1)
{
    return it - n;
}

} // namespace mystd