簡単な世代間血液型割合の変化のシミュレート。

blood.rb

class Blood
  def initialize f, g
    @blood = [f, g].sort
  end

  def type
    case @blood
    when %w(A A) then "A"
    when %w(A O) then "A"
    when %w(B B) then "B"
    when %w(B O) then "B"
    when %w(O O) then "O"
    when %w(A B) then "AB"
    end
  end

  def blood
    @blood.join
  end

  def meiosis
    @blood.sample
  end
end

class Pair
  attr_reader :pair
  def initialize x, y
    @pair = [x, y]
  end

  def children
    Blood.new(*@pair.map(&:meiosis))
  end
end

class Japan
  # 300
  A, B, O, AB = [38, 22, 31, 9].map(&3.method(:*))

  AA = A / 3
  AO = (A / 3) * 2
  BB = B / 3
  BO = (B / 3) * 2

  def initialize
    aa = [Blood.new("A", "A")] * AA
    ao = [Blood.new("A", "O")] * AO
    bb = [Blood.new("B", "B")] * BB
    bo = [Blood.new("B", "O")] * BO
    oo = [Blood.new("O", "O")] * O
    ab = [Blood.new("A", "B")] * AB
    @people = [*aa, *ao, *bb, *bo, *oo, *ab] * 10
  end

  def step
    @people = @people.shuffle.each_cons(2).map {|x, y|
      Pair.new(x, y).children
    }.flatten
  end

  def show
    size = @people.size
    bloods = %w(AA AO BB BO OO AB)
    bloods.each do |blood|
      puts "blood #{blood}: #{@people.select{|person| person.blood == blood}.size.to_f / size}"
    end

    types = %w(A B O AB)
    types.each do |type|
      puts "type #{type}: #{@people.select{|person| person.type == type}.size.to_f / size}"
    end
  end
end

class Generations
  def initialize
    japan = Japan.new
    n = 100
    n.times do
      japan.step
    end
    puts "#{300}人"
    puts n.to_s + "ステップ"
    japan.show
  end
end

Generations.new