class DeCody
  def initialize(key); @key = key.downcase.gsub(/[^a-z]/,'') end
  def locate(letter); [@key.index(letter)/5, @key.index(letter)%5] end
  def at(row, col); @key[(row*5) + col, 1] end
  def encode(str); pairs, str = [], str.downcase.gsub(/[^a-z]/,'')
    str.scan(/..|./) do |pair|
      if pair.length == 1;        pairs += [pair + "x"]
      elsif pair =~ /([a-z])\1/;  pairs += ["#{$1}q", "#{$1}q"]
      else                        pairs += [pair] end
    end
    pairs.collect do |pair|
      l1, l2 = locate(pair[0,1]), locate(pair[1,1])
        if l1.first == l2.first # on the same column
          l1[1], l2[1] = (l1[1] + 1) % 5, (l2[1] + 1) % 5
        elsif l1.last == l2.last # on the same row
          l1[0], l2[0] = (l1[0] + 1) % 5, (l2[0] + 1) % 5
        else; l1[1], l2[1] = l2[1], l1[1] end # normal swap
        [at(*l1), at(*l2)]
    end.join
  end
  def decode(str); pairs, str = [], str.downcase.gsub(/[^a-z]/,'')
    str.scan(/..|./) do |pair|
      if pair.length == 1;        pairs += [pair + "x"]
      elsif pair =~ /([a-z])\1/;  pairs += ["#{$1}q", "#{$1}q"]
      else                        pairs += [pair] end
    end
    pairs.collect do |pair|
      l1, l2 = locate(pair[0,1]), locate(pair[1,1])
        if l1.first == l2.first # on the same column
          l1[1], l2[1] = (l1[1] - 1) % 5, (l2[1] - 1) % 5
        elsif l1.last == l2.last # on the same row
          l1[0], l2[0] = (l1[0] - 1) % 5, (l2[0] - 1) % 5
        else; l1[1], l2[1] = l2[1], l1[1] end # normal swap
        [at(*l1), at(*l2)]
    end.join
  end
end

dc = DeCody.new <<-END
k x z p w
i g t f a
h o s e n
y m b r c
u l q d v
END

p dc.decode("le hs sq dr iw ai bs ka is ni cg ev do to")