Ruby Integer to English from http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/135449

gistfile1.rb

#!/usr/bin/ruby

class Integer

   Ones = %w[ zero one two three four five six seven eight nine ]
   Teen = %w[ ten eleven twelve thirteen fourteen fifteen
              sixteen seventeen eighteen nineteen ]
   Tens = %w[ zero ten twenty thirty forty fifty
              sixty seventy eighty ninety ]
   Mega = %w[ none thousand million billion ]

   def to_english
     places = to_s.split(//).collect {|s| s.to_i}.reverse
     name = []
     ((places.length + 2) / 3).times do |p|
       strings = Integer.trio(places[p * 3, 3])
       name.push(Mega[p]) if strings.length > 0 and p > 0
       name += strings
     end
     name.push(Ones[0]) unless name.length > 0
     name.reverse.join(" ")
   end

   private

   def Integer.trio(places)
     strings = []
     if places[1] == 1
       strings.push(Teen[places[0]])
     elsif places[1] and places[1] > 0
       strings.push(places[0] == 0 ? Tens[places[1]] :
                    "#{Tens[places[1]]}-#{Ones[places[0]]}")
     elsif places[0] > 0
       strings.push(Ones[places[0]])
     end
     if places[2] and places[2] > 0
       strings.push("hundred", Ones[places[2]])
     end
     strings
   end

end

# If there are command-line args, just print out English names.
if ARGV.length > 0
   ARGV.each {|arg| puts arg.to_i.to_english}
   exit 0
end

# Return the name of the number in the specified range that is the
# lowest lexically.
def minimum_english(start, stop, incr)
   min_name = start.to_english
   start.step(stop, incr) do |i|
     name = i.to_english
     min_name = name if min_name > name
   end
   min_name
end

# Find the lowest phrase for each 3-digit cluster of place-values.
# The lowest overall string must be composed of elements from this list.
components =
   [ minimum_english(10**9, 10**10, 10**9),
     minimum_english(10**6, 10**9 - 1, 10**6),
     minimum_english(10**3, 10**6 - 1, 10**3),
     minimum_english(10**0, 10**3 - 1, 2) ]

$result = components[-1]
def search_combinations(list, selected = [])
   if elem = (list = list.dup).shift
     if list.empty?
       # Always include the final element from list in the selection.
       string = selected.dup.push(elem).join(" ")
       $result = string if $result > string
     else
       search_combinations(list, selected)
       search_combinations(list, selected.dup.push(elem))
     end
   end
   $result
end

puts search_combinations(components)