Maxchars - Given a string, find the character that occurs most frequently.

maxchars.exs

defmodule Maxchar do
  @moduledoc """
  Given a string, return the character that occurs most frequently
  """
  def main(str) when is_binary(str) do
    str
    |> count_chars()
    |> print()
  end

  defp count_chars(string) do
    count_chars(String.graphemes(string), Map.new())
  end

  defp count_chars([], map), do: map

  defp count_chars([first | rest], map) do
    case Map.has_key?(map, first) do
      true ->
        map = Map.update!(map, first, fn val -> val + 1 end)
        count_chars(rest, map)

      false ->
        map = Map.put_new(map, first, 1)
        count_chars(rest, map)
    end
  end

  defp print(map) do
    map
    |> Enum.max_by(fn {char, value} -> value end)
  end
end