_NN>void duplicate(std::vector<int>& v)
_NN>{
_NN>  size_t i = 0;
_NN>  size_t count = v.size();
_NN>  for (auto const& e : v)
_NN>  {
_NN>    if (i == count)
_NN>      break;
_NN>    v.push_back(e);
_NN>    i++;
_NN>  }
_NN>}
_NN>