std::experimental::ranges::search_n

template<ForwardIterator I, Sentinel<I> S, class T,
         class Pred = ranges::equal_to<>, class Proj = ranges::identity>
    requires IndirectlyComparable<I, const T*, Pred, Proj>
I search_n(I first, S last, ranges::difference_type_t<I> count,
           const T& value, Pred pred = Pred{}, Proj proj = Proj{})
{
    for (; first != last; ++first)
    {
        if (!ranges::invoke(pred, ranges::invoke(proj, *first), value))
            continue;
 
        I candidate = first;
        ranges::difference_type_t<I> cur_count = 0;
 
        while (true)
        {
            ++cur_count;
            if (cur_count == count)
                // success
                return candidate;
 
            ++first;
            if (first == last)
                // exhausted the list
                return first;
 
            if (!ranges::invoke(pred, ranges::invoke(proj, *first), value))
                // too few in a row
                break;
        }
    }
    return first;
}