Roman Numeral

roman_numeral.rb

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

DEC_TO_NUMERAL_MAP = NUMERAL_MAP.invert

def tokenize_roman_numerals(roman_numeral)
  output = []
  len = roman_numeral.length
  index = 0
  while(index < len)
    mrn, indx_delta = max_roman_numeral(roman_numeral[index...(index+2)])
    output << mrn
    index = index + indx_delta
  end
  output
end

def max_roman_numeral(expression)
  NUMERAL_MAP.keys.each do |roman_letter|
    if roman_letter == expression
      return [roman_letter, 2]
    end
  end
  NUMERAL_MAP.keys.each do |roman_letter|
    if roman_letter == expression[0]
      return [roman_letter, 1]
    end
  end
end

# puts tokenize_roman_numerals("MCMXCIX")
# ["M", "CM", "XC", "IX"]

def from_roman(roman_numeral)
  output = 0
  tokenize_roman_numerals(roman_numeral).each do |rn_token|
    output = output + NUMERAL_MAP[rn_token]
  end
  output
end

def to_roman(num)
  output = ""
  DEC_TO_NUMERAL_MAP.keys.each do |dec|
    break if num == 0
    if num >= dec
      output = output + DEC_TO_NUMERAL_MAP[dec]
      num = num - dec
    end
  end
  output
end

# puts to_roman(1999)
# MCMXCIX

puts from_roman('MCMXCIX')
puts from_roman('XXXVII')