Number words to number

number_convert.rb

#!/usr/bin/env rspec

require 'rubygems'
require 'bundler/setup'
require 'rspec'

class Convert
  
  MAPPING = {
    # singles
    'zero'  => 0,
    'one'   => 1,
    'two'   => 2,
    'three' => 3,
    'four'  => 4,
    'five'  => 5,
    'six'   => 6,
    'seven' => 7,
    'eight' => 8,
    'nine'  => 9,
    'ten'   => 10,
    # teens
    'eleven'    => 11,
    'twelve'    => 12,
    'thirteen'  => 13,
    'fourteen'  => 14,
    'fifteen'   => 15,
    'sixteen'   => 16,
    'seventeen' => 17,
    'eighteen'  => 18,
    'nineteen'  => 19,
    # tens
    'twenty'  => 20,
    'thirty'  => 30,
    'forty'   => 40,
    'fifty'   => 50,
    'sixty'   => 60,
    'seventy' => 70,
    'eighty'  => 80,
    'ninety'  => 90,
    # bigger numbers
    'hundred'  => 100,
    'thousand' => 1000,
    'million'  => 1000000
  }
  
  THOUSANDS = {
    'thousand' => true,
    'million' => true,
  }
  
  def self.to_number(words)
    parts = words.split(/[-,\s]+/)
    result = 0
    accum = 0
    while true
      last_word = parts.shift
      next if last_word == 'and'
      last = MAPPING[last_word]
      raise "Unknown word #{last_word}" unless last
      if last_word == 'hundred'
        accum = 1 if accum == 0
        accum *= 100
      elsif THOUSANDS[last_word]
        accum = 1 if accum == 0
        result += accum * last
        accum = 0
      else
        accum += last
      end
      return result + accum if parts.size == 0
    end
  end
  
end

describe Convert do

  begin
    <<-EOF
      three                         = 3
      fourteen                      = 14
      fifty two                     = 52
      eight hundred sixty-nine      = 869
      thirteen hundred              = 1300
      four million, thirty two      = 4000032
      hundred seventy three million, two hundred five thousand, three hundred seven = 173205307
    EOF
  end.strip.split("\n").each do |line|
    words, number = line.split('=')
    words.strip!; number.strip!
    it "'#{words}' should == #{number}" do
      Convert.to_number(words).should == number.to_i
    end
  end

end