gistfile1.rb

#!/usr/bin/env ruby

# monte carlo simulation for mini

class Mini
  attr_reader :score

  def initialize(p)
    @p = p
    @score = [0, 0]
  end

  def play
    @team = 0 # start with team 0
    self.play_point
  end

  def play_point
    if rand < @p # scored!
      @score[@team] += 1
    else # turnover!
      @score[@team] -= 1
      @team = (@team + 1) % 2
    end

    self.play_point unless self.over?
  end

  def over?
    score.include?(3) or score.include?(-2)
  end

  def reset
    @score = [0, 0]
  end
end

n = 100_000
scores = Hash.new { 0 }
m = Mini.new(0.5)
n.times do
  m.reset
  m.play
  scores[m.score] += 1
end

scores.sort.reverse.each do |k,v|
  puts "#{k.to_s.ljust(8)}: #{v / n.to_f}"
end

print "Winning %: "
puts scores.select {|k,_| k[0] == 3 or k[1] == -2 }.values.inject {|n,i| n + i } / n.to_f