README

Game Of Life in Ruby

initialize function gives a few options. You can specify the dimensions
of the board, and you can specify if you want the board to wrap around
to the other side.

evolve simply iterates though the state array and uses the rules to
determine if it should change states.

randomize_game_state is in a separate function, so it can easily be
called if desired.

is_alive returns false if you give it a cell off the board. Also you
can specify an origin cell and check a cell's state relative to it with
optional parameters.

count_neighbours simply counts all the alive cells around a particular
cell, using alive relative feature to simplify this.

update_dimensions if you set the state to an arbitrary array, this 
method can be called to properly set the width and height. It uses the
smallest column height to avoid problems.

game_of_life.rb

class GameOfLife

  attr_accessor :state

  DEAD = 0
  ALIVE = 1

  def initialize(width, height = width, wrapped = true)
    @wrapped = wrapped
    randomize_game_state(width, height)
  end

  def evolve
    # Copy game state
    new_state = Marshal.load(Marshal.dump(@state))
    
    0.upto(@width - 1) do |x| 
      0.upto(@height - 1) do |y|
        neighbours = count_neighbours(x, y)
        if is_alive(x, y) and neighbours < 2
          new_state[x][y] = DEAD
        elsif is_alive(x, y) and neighbours > 3
          new_state[x][y] = DEAD
        elsif !is_alive(x, y) and neighbours == 3
          new_state[x][y] = ALIVE
        end  
      end 
    end

    @state = new_state
  end
  
  def randomize_game_state(width, height)
    @width = width
    @height = height
    @state = Array.new(@width) { Array.new(@height) { rand(2) } }
  end

  def is_alive(x, y, rel_x = 0, rel_y = 0)
    cx = x + rel_x
    cy = y + rel_y
    if @wrapped
      cx %= @width
      cy %= @height
    else 
      # return if out of range
      return false if cx >= @width  or cx <  0 or
                      cy >= @height or cy <  0
    end
    state[cx][cy] == ALIVE
  end

  def count_neighbours(x, y)
    neighbours = 0
    neighbours += 1 if is_alive(x, y, 1, 0)   # East
    neighbours += 1 if is_alive(x, y, 1, 1)   # North East
    neighbours += 1 if is_alive(x, y, 0, 1)   # North
    neighbours += 1 if is_alive(x, y, -1, 1)  # North West
    neighbours += 1 if is_alive(x, y, -1, 0)  # West
    neighbours += 1 if is_alive(x, y, -1, -1) # South West
    neighbours += 1 if is_alive(x, y, 0, -1)  # South
    neighbours += 1 if is_alive(x, y, 1, -1)  # South East
    neighbours
  end

  def update_dimensions
    width = @state.length
    height = @state[0].length
    # Find minimum height
    1.upto(width - 1) do |x|
      height = @state[x].length if height > @state[x].length
    end
    @width = width
    @height = height
  end

end