john_and_ann.ex

defmodule Johnann do
  
  def john(n) when n >= 1 do
  	john_and_ann(n)[:john]
  end
  
  def ann(n) when n >= 1 do
  	john_and_ann(n)[:ann]
  end
  
  def sum_john(n) when n >= 1 do
    john(n) |> Enum.sum
  end
  
  def sum_ann(n) when n >= 1 do
  	ann(n) |> Enum.sum
  end
  
  defp john_and_ann(n, katas \\ %{john: %{0 => 0}, ann: %{0 => 1}}) do
  	k = map_size(katas[:john])
    if k < n do
    	john = Map.put(katas[:john], k, k - katas[:ann][katas[:john][k-1]])
    	ann  = Map.put(katas[:ann],  k, k - katas[:john][katas[:ann][k-1]])
      john_and_ann(n, %{ john: john, ann: ann })
    else
    	katas
    end
  end
  
end