Returns all the possible letter combinations for a given phone numbah.

phone_numbah.rb

##
# To run:
# irb > require '[PATH_TO_FILE]/phone_numbah'
# irb > PhoneNumbah.show_possibilities [PHONE_NUMBAH]
##

class PhoneNumbah
  Digits = { "1" => ["1"],
             "2" => ["A", "B", "C"],
             "3" => ["D", "E", "F"],
             "4" => ["G", "H", "I"],
             "5" => ["J", "K", "L"],
             "6" => ["M", "N", "O"],
             "7" => ["P", "Q", "R", "S"],
             "8" => ["T", "U", "V"],
             "9" => ["W", "X", "Y", "Z"],
             "0" => ["0"],
            }

  # Takes an integer phone number of 10 digits ie. 6176100089
  def self.show_possibilities numbah
    split_numbah = numbah.to_s.split ''

    digit_letters = split_numbah.map { |digit| Digits[digit] }

    digit_letters[0].product(*digit_letters[1..-1]).map { |combo| combo.join('') }
  end
end