Elixir fibonacci #1

fib.exs

defmodule Fib do 
  def fib(0) do 0 end
  def fib(1) do 1 end
  def fib(n) do fib(n-1) + fib(n-2) end
end

IO.puts Fib.fib(10)

I implemented it using a top-down approach while utilizing memoization to avoid redundant calculations.

defmodule Fib do
  def run(n) do
    {result, _} = do_run(n, %{})

    result
  end

  defp do_run(n, memo) when n in [1, 2] do
    result_with_memo(n, 1)
  end

  defp do_run(n, memo) do
    case memo[n] do
      nil ->
        {result1, memo} = do_run(n - 1, memo)
        {result2, memo} = do_run(n - 2, memo)

        result_with_memo(n, result1 + result2)

      result ->
        {result, memo}
    end
  end

  defp result_with_memo(n, result) do
    {result, memo |> Map.put(n, result)}
  end
end