exercism/elixir/collatz-conjecture/lib/collatz_conjecture.ex

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2024-06-27 03:06:52 +00:00
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