void permutations(std::string s, int pos = 0)
{
    if (pos >= s.size())
    {
        std::cout << s << 'n';
        return;
    }
    else
    {
        for (int i = pos; i < s.size(); ++i)
        {
            std::swap(s[i], s[pos]);
            permutations(s, pos + 1);
            std::swap(s[i], s[pos]);
        }
    }
}