defmodule Hamming do
  @doc """
  Returns number of differences between two strands of DNA, known as the Hamming Distance.

  ## Examples

  iex> Hamming.hamming_distance(~c"AAGTCATA", ~c"TAGCGATC")
  {:ok, 4}
  """
  @spec hamming_distance([char], [char]) :: {:ok, non_neg_integer} | {:error, String.t()}
  def hamming_distance(strand1, strand2) when length(strand1) != length(strand2), do: {:error, "strands must be of equal length"}
  def hamming_distance(strand1, strand2) do
    {:ok, Enum.count(Enum.zip(strand1, strand2), fn {s1, s2} -> s1 != s2 end)}
  end
end