Roman to Arabic number converter

gistfile1.rb

input = "MCMXCIX" # 1999

# Roman to Arabic mapper
r2a = {"I" => 1, "V" => 5, "X" => 10, "L" => 50, "C" => 100, "D" => 500, "M" => 1000}

# Translate input to an array of arabic numbers
numbers = input.split(//).map {|c| r2a[c]}
count = numbers.count-1

# Compute result (more infos @ http://en.wikipedia.org/wiki/Roman_numerals)
result = 0
(0..count).each do |i|
  if i != count and numbers[i] < numbers[i+1]
  	result -= numbers[i]
  else
  	result += numbers[i]
  end 
end

puts result