game_of_life.rb

class GameOfLife
  def initialize(alive = [2, 3], born = [3])
    @generation = {}
    @generations = 0
    @alive = alive
    @born = born
  end

  def add_neighbour(pos)
    if cell = @generation[pos]
      cell[:neighbours] = (cell[:neighbours] or 0) + 1
    else
      @generation[pos] = { :alive => false, :neighbours => 1 }
    end
  end

  def next_gen
    @generations += 1
    @generation.dup.each_key do |pos|
      [[-1, -1], [0, -1], [1, -1],
       [-1,  0],          [1,  0],
       [-1,  1], [0,  1], [1,  1]].each do |d|
        add_neighbour([pos[0] + d[0], pos[1] + d[1]])
      end
    end
    @generation.delete_if do |pos, cell| 
      cell[:alive] = false unless @alive.include?(cell[:neighbours])
      cell[:alive] = true if @born.include?(cell[:neighbours])
      cell[:neighbours] = 0
      not cell[:alive]
    end
  end
end