game_of_life.rb

# Alogirthm for Game of Life 
# Check more details here - http://en.wikipedia.org/wiki/Conway%27s_Game_of_Life

class GameOfLife
  attr_accessor :matrix, :rows, :columns

  def initialize rows, columns
    @rows, @columns = rows, columns
    @matrix = []
    rows.times do |row|
      @matrix[row] ||= []
      columns.times do |column|
        @matrix[row][column] = false
      end
    end
  end

  def next_tick
    new_matrix = []
    rows.times do |row|
      new_matrix[row] ||= []
      columns.times do |column|
        alive_neighbours_count = neighbours(row, column).count(true)
        if !self.matrix[row][column] && alive_neighbours_count == 3
          new_matrix[row][column] = true
        elsif self.matrix[row][column] && alive_neighbours_count != 2 && alive_neighbours_count != 3
          new_matrix[row][column] = false
        else
          new_matrix[row][column] = self.matrix[row][column]
        end
      end
    end
    self.matrix = new_matrix
  end

  def print_cells
    rows.times do |row|
      columns.times do |column|
        matrix[row][column] ? print("O") : print("-")
      end
      print "\n"
    end
    print "\n"
  end

  def neighbours row, column
    neighbours = []
    rows_limit = matrix.count - 1
    columns_limit = matrix[0].count - 1
    ([0, row-1].max..[rows_limit, row+1].min).to_a.each do |row_index|
      ([0, column-1].max..[columns_limit, column+1].min).to_a.each do |column_index|
        neighbours << matrix[row_index][column_index] unless row_index == row && column_index == column
      end
    end
    neighbours
  end
end

game = GameOfLife.new(100, 100)

# set alive cells
game.matrix[0][0] = true
game.matrix[0][1] = true
game.matrix[1][0] = true
game.matrix[1][3] = true
game.matrix[2][1] = true
game.matrix[2][2] = true

game.print_cells

5.times do
  game.next_tick
  game.print_cells
end