My solution for RPCFN #11: The Game of Life

game_of_life.rb

require 'rubygems'

class GameOfLife
    attr_accessor :state, :tmp_state 
        
    def initialize(size)
      @size  = size
      @state = Array.new(@size){ Array.new @size }
      @size.times{ |row| @size.times{ |column| @state[row][column] = rand(2) } }
      @tmp_state = @state.clone
    end
	
   def evolve
     @state.each_index do |x| 
       @state[x].each_index do |y|
         minus_x = x - 1
     	 minus_y = y - 1
       	 plus_x  = x + 1
       	 plus_y  = y + 1
       	 plus_y  = 0 if plus_y >= @size
       	 plus_x  = 0 if plus_x >= @size
       	 live_neighbours = 0

	 live_neighbours += 1 if @state[minus_x][minus_y] == 1 
	 live_neighbours += 1 if @state[minus_x][y] == 1
	 live_neighbours += 1 if @state[minus_x][plus_y] == 1
	   			  
	 live_neighbours += 1 if @state[x][minus_y] == 1
	 live_neighbours += 1 if @state[x][plus_y] == 1
 
	 live_neighbours += 1 if @state[plus_x][minus_y] == 1
	 live_neighbours += 1 if @state[plus_x][y] == 1
	 live_neighbours += 1 if @state[plus_x][plus_y] == 1
 			 
	 case live_neighbours
       	   when 0..1  then @tmp_state[x][y] = 0
       	   when 3     then @tmp_state[x][y] = 1
	   when 4..90 then @tmp_state[x][y] = 0
       	 end
       end
     end
     @state = @tmp_state.clone
   end
end

game_of_life_test.rb

require File.join(File.dirname(__FILE__), 'game_of_life')
require 'rubygems'
require 'test/unit'

class GameOfLifeTest < Test::Unit::TestCase

  def setup
    @game = GameOfLife.new(3)
  end
  
  def test_should_kill_with_no_neighbours
    @game.state     = [[1,0,0],[0,0,0],[0,0,0]]
    @game.tmp_state = [[1,0,0],[0,0,0],[0,0,0]]
    after = @game.evolve
    assert_equal after[0][0], 0
  end
  
 def test_should_kill_with_just_one_neighbour
    @game.state     = [[0,0,0],[1,0,0],[1,0,0]]
    @game.tmp_state = [[0,0,0],[1,0,0],[1,0,0]]
    after = @game.evolve
    assert_equal after[1][0], 0
    assert_equal after[2][0], 0
  end
  
  def test_should_kill_with_more_than_3_neighbours
    @game.state     = [[1,1,1],[1,1,1],[1,1,1]]
    @game.tmp_state = [[1,1,1],[1,1,1],[1,1,1]]
    after = @game.evolve
    assert_equal after, [[0,0,0],[0,0,0],[0,0,0]]
  end
  
  def test_should_give_birth_if_3_neighbours
    @game.state     = [[1,0,0],[1,1,0],[0,0,0]]
    @game.tmp_state = [[1,0,0],[1,1,0],[0,0,0]]
    after = @game.evolve
    assert_equal after, [[1,1,1],[1,1,1],[1,1,1]]
  end
  
  def test_should_keep_alive_if_2_neighbours
    @game2 = GameOfLife.new(4)
    @game2.state     = [[0,0,0,0],[0,0,1,0],[0,1,1,0],[0,0,0,0]]
    @game2.tmp_state = [[0,0,0,0],[0,0,1,0],[0,1,1,0],[0,0,0,0]]
    after = @game2.evolve
    assert_equal after[1][2], 1
    assert_equal after[2][1], 1
    assert_equal after[2][2], 1
    assert_equal after, [[0, 0, 0, 0], [0, 1, 1, 0], [0, 1, 1, 0], [0, 0, 0, 0]]
  end
  
  def test_should_initiate_with_rand_numbers_0_or_1
    group1 = @game.state.clone
    @game  = GameOfLife.new(3) 
    group2 = @game.state.clone
    assert_not_equal group1, group2
  end
  
end