playing_with_passphrases.rb

def play_pass(str, n)
  str.chars.map do |l|
    if l =~ /[A-Za-z]/
      ar = [l]
      n.to_i.times { |x| ar << ar.last.next}
      ar.last[-1]
    elsif l =~ /\d/
      9 - l.to_i
    else
      l
    end
  end.map.with_index { |x, i| i.odd? ? x.to_s.downcase : x }.reverse.join
end
  

# Everyone knows passphrases. One can choose passphrases from poems, songs, movies names and so on but frequently 
# they can be guessed due to common cultural references. You can get your passphrases stronger by different means. One is the following:

# choose a text in capital letters including or not digits and non alphabetic characters,

# shift each letter by a given number but the transformed letter must be a letter (circular shift),
# replace each digit by its complement to 9,
# keep such as non alphabetic and non digit characters,
# downcase each letter in odd position, upcase each letter in even position (the first character is in position 0),
# reverse the whole result.
# Example:
# your text: "BORN IN 2015!", shift 1

# 1 + 2 + 3 -> "CPSO JO 7984!"

# 4 "CpSo jO 7984!"

# 5 "!4897 Oj oSpC"

# With longer passphrases it's better to have a small and easy program. Would you write it?