euler20.rb

   1 class Integer
   2   def factorial
   3     Array.new(self) {|i| i + 1}.reduce(:*)
   4   end
   5 end
   6
   7 if __FILE__==$0
   8   puts 100.factorial.to_s.scan(/./).map{|s| s.to_i}.reduce(:+)
   9 end