decode_words2.rb

LETTER_MAP = ('a'..'z').to_a

def decode_word_faster(word, current_word=[], words=[])
  if word.size == 0 # we reached the end of word
    words.push(current_word.map{ |letter| LETTER_MAP[letter-1] }.join)
    return words
  end
  decode_word_faster(word[1..-1], current_word.clone.push(word[0].to_i), words)
  if word.size > 1 && (word[0..1].to_i < 26)
    decode_word_faster(word[2..-1], current_word.clone.push(word[0..1].to_i), words)
  end
  return words
end

p decode_word_faster('2114111925')