roman_numerals.rb

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

def to_roman(number)
  result = ''
  NUMERALS.each do |roman, arabic|
    div, number = number.divmod(arabic)
    result << (roman.to_s * div)
  end
  result
end

def test_drive
  puts "My totally sweet testing script:"
  puts ""
  puts "input | expected | actual"
  puts "------|----------|-------"
  puts "4     | IV       | #{to_roman(4)}"
  puts "9     | IX       | #{to_roman(9)}"
  puts "13    | XIII     | #{to_roman(13)}"
  puts "1453  | MCDLIII  | #{to_roman(1453)}"
  puts "1646  | MDCXLVI  | #{to_roman(1646)}"
end