puzzle.rb

#!/usr/bin/env ruby

class Fixnum
  def holes
    if abs > 9
      to_s.chars.reduce(0) { |a, e| a += e.to_i.holes }
    else
      case self
      when 1, 2, 3, 5, 7
        0
      when 0, 4, 6, 9
        1
      else
        2
      end
    end
  end
end

5.times do
  n = (1..1_000_000).to_a.sample
  puts "#{n}: #{n.holes}"
end