dna.ex

defmodule DNA do
  @doc ~S"""
  Count the respective number of times that the symbols 'A', 'C', 'G', and 'T' in a given string.
  
  Returns the count as four integers separated by spaces, representing occureneces of "A", "C", "G", and "T" respectively.
  
  ## Examples
  
      iex> DNA.count("AGCTTTTCATTCTGACTGCAACGGGCAATATGTCTCTGTGTGGATTAAAAAAAGAGTGTCTGATAGCAGC")
      "20 12 17 21"
  """
  @spec count(string :: String.t) :: String.t
  def count(string), do: _count(string, [0,0,0,0])
  def _count("", [a,c,g,t]), do: "#{a} #{c} #{g} #{t}"
  def _count("A" <> rest, [a,c,g,t]), do: _count(rest, [a+1,c,g,t])
  def _count("C" <> rest, [a,c,g,t]), do: _count(rest, [a,c+1,g,t])
  def _count("G" <> rest, [a,c,g,t]), do: _count(rest, [a,c,g+1,t])
  def _count("T" <> rest, [a,c,g,t]), do: _count(rest, [a,c,g,t+1])
end