game of life.rb

module Enumerable
  def bag
    # [1,1,1,1,2,2,3] => {1 => 4, 2 => 2, 3 => 1}
    # similar to python's Counter
    Hash[group_by { |x| x }.map {|k, v| [k, v.count] }]
  end
end

def print(grid)
  system('clear')
  min_x, max_x = grid.keys.map(&:first).minmax
  min_y, max_y = grid.keys.map(&:last).minmax

  result = min_y.upto(max_y).map do |y|
     min_x.upto(max_x).map do |x|
      grid[[x,y]] ? 'X' : ' '
    end.to_a.join("")
  end.to_a.join("\n")

  puts result
end

def neighbors_of(location)
  x_range = (location.first-1).upto(location.first+1).to_a
  y_range = (location.last-1).upto(location.last+1).to_a
  x_range.product(y_range) - [location]
end

def will_be_alive(was_alive, neighbors_count)
  if was_alive
    [2,3].include? neighbors_count
  else
    neighbors_count == 3
  end
end

def iterate(old_grid)
  old_grid.flat_map do |loc, _|
    neighbors_of(loc)
  end.bag.select do |loc, alive_near_me|
    will_be_alive(old_grid[loc], alive_near_me)
  end
end

def new_grid()
  glider = [[1,0], [1, 2], [0,2], [2,2], [2,1]]
  box = [[-3,3], [-3,4], [-4,3], [-4,4]]
  alive_start = glider + box
  Hash[alive_start.map { |k| [k, true] }]
end

grid = new_grid()

until grid.empty? do
  print(grid)
  grid = iterate(grid)
  sleep 1
end