сollatz-сonjecture

elixir/collatz-conjecture/lib/collatz_conjecture.ex

@@ -0,0 +1,15 @@
+defmodule CollatzConjecture do
+  @doc """
+  calc/1 takes an integer and returns the number of steps required to get the
+  number to 1 when following the rules:
+    - if number is odd, multiply with 3 and add 1
+    - if number is even, divide by 2
+  """
+  @spec calc(input :: pos_integer()) :: non_neg_integer()
+  def calc(input) when is_integer(input) and input > 0, do: collatz(input)
+
+  defp collatz(input, steps \\ 0)
+  defp collatz(1, steps), do: steps
+  defp collatz(input, steps) when rem(input, 2) == 0, do: collatz(div(input, 2), steps + 1)
+  defp collatz(input, steps), do: collatz(input * 3 + 1, steps + 1)
+end