By @okitan and @june29 on http://regional.rubykaigi.org/minato01

amida.rb

#!/usr/bin/env ruby

class Amida
  def initialize(number)
    @number = number
    @depth  = number * 2
    @goal   = rand(number)
    @data   = generate
  end

  def render
    puts @number.times.to_a.map { |n| "%c" % (n + 65) }.join("   ")

    @data.each do |line|
      puts [ nil, *line.map { |e| e == 1 ? "---" : "   " }, nil ].join("|")
    end

    puts " " * (@goal * 4) + "*"
  end

  private
  def generate
    loop do
      prev = 0

      amida = @depth.times.map { |i|
        (@number - 1).times.map { |j|
          if prev == 1
            prev = 0
          else
            prev = rand(100) < 22 ? 1 : 0
          end
        }
      }.to_a

      return amida if amida.transpose.all? { |line| line.inject(&:+) > 0 }
    end
  end
end

n = (ARGV[0] || 5).to_i

amida = Amida.new(n)
amida.render