The Birthday Problem!

gistfile1.rb

lower_bound = (ARGV.shift || 2).to_i
upper_bound = (ARGV.shift || 35).to_i
iterations = (ARGV.shift || 20_000).to_i

(lower_bound..upper_bound).each do |person_count|
  matches = 0
  iterations.times do
    matches += 1 if (1..person_count).map{|p| rand(365)}.uniq!
  end
  puts "Person count: %3d Success: %3.1f" %
    [person_count, matches * 100.0 / iterations]
end

__END__

$ ruby birthday.rb 22 24
Person count:  22 Success: 47.6
Person count:  23 Success: 50.6
Person count:  24 Success: 54.0