hacky_list_subset.exs

defmodule ListSubset do

  defp _contains_letters_count([], _, acc), do: acc

  defp _contains_letters_count([h|t], compare, acc) do
    new_list = List.delete(compare, h)
    diff = length(compare) - length(new_list)
    _contains_letters_count(t, new_list, acc+diff)
  end

  def is_subset(str1, str2) do
    count = _contains_letters_count(str1, str2, 0)
    count == length(str2)
  end

end

ListSubset.is_subset('hello', 'leoh') # true
ListSubset.is_subset('hello', 'leohh') # false