finally.rb

def num_search(string, ans)
  if (string.empty?)
    ans[:count] += 1
    return
  end
  return if string[0] == "0"
  num_search(string[1..-1], ans)
  if (string.length > 1 and (string[0].to_i < 2 or (string[0].to_i == 2 and string[1].to_i < 7)))
    num_search(string[2..-1], ans)
  end
end

def num_decodings(string)
  return 0 if string.empty? or string[0] == "0"
  ans = {:count => 0}
  num_search(string, ans)
  return ans[:count]
end