janken.rb

class Hand
  @@HANDS = ['G', 'T', 'P']
  @@WIN = 2
  @@LOSE = 1
  @@DRAW = 0

  attr_reader :int_hand, :str_hand

  def initialize(str_hand)
    @str_hand = str_hand
    @int_hand = Hand.to_int(str_hand)
    raise 'Unrecognized hand #{str_hand}' if @int_hand.nil?
  end

  def janken(urhand)
    (@int_hand - urhand.int_hand + 3) % 3
  end
  
  def get_superior
    int_sup_hand = (@int_hand + 2) % 3
    Hand.new(Hand.to_string(int_sup_hand))
  end
  
  def to_s
    @str_hand
  end

  def self.WIN; @@WIN; end
  def self.LOSE; @@LOSE; end
  def self.DRAW; @@DRAW; end

  private
  def self.to_int(str_hand)
    @@HANDS.index(str_hand)
  end
  
  def self.to_string(int_hand)
    @@HANDS[int_hand]
  end
end

ur_hands = ARGV[0].split('').map{|v| Hand.new(v)}
first_hand = Hand.new('G')

my_hands = ur_hands.inject([first_hand]) do |mine, ur_hand|
  case mine.last.janken(ur_hand)
    when Hand.DRAW, Hand.LOSE
        mine << mine.last.get_superior
    when Hand.WIN
        mine << mine.last
  end
  mine
end

my_hands[0..-2].each do |v|
   puts v.to_s 
end