Odd = Red Ball, Even = Blue Ball

balls.rb

# The adding logic seems to dictate the result.  So if you start with 1 ball each (differnt colors / odd),
# you end up with red.  
blue_balls = Array.new(17, 'blue')
red_balls  = Array.new(17, 'red')

balls = red_balls + blue_balls

balls.shuffle!
puts "Starting Ball List: #{balls}"

while balls.count > 1
  take_2 = balls.shift(2)
  puts "grabbing 2 balls: #{take_2}"
  if take_2.uniq.count    == 1  # balls are the same color
    balls.push('blue')          # add a blue ball back
    puts "+1 blue"
  elsif take_2.uniq.count == 2  # balls are differnt colors
    balls.push('red')           # add a red ball back
    puts "+1 red"
  end
end

puts "Last Ball Remaining: #{balls}"