roman_numerals.rb

ROMAN_MAP = {
  1 => "I",
  4 => "IV",
  5 => "V",
  9 => "IX",
  10 => "X",
  40 => "XL",
  50 => "L",
  90 => "XC",
  100 => "C",
  400 => "CD",
  500 => "D",
  900 => "CM",
  1000 => "M" }

def to_roman(i)
  ROMAN_MAP.sort {|a,b| a[0] <=> b[0] }.reverse.collect do |k,v|
    times, i = i.divmod(k)
    v * times
  end.join("")
end

def from_roman(s)
  inverted_map = ROMAN_MAP.invert
  s.split(//).collect do |n|
    inverted_map[n]
  end.inject()
end