roman.rb

BASIC_NUMERALS = {
  1000 => "M",
  500  => "D",
  100  => "C",
  50   => "L",
  10   => "X",
  5    => "V",
  1    => "I",
}

NUMERAL_VALUES = BASIC_NUMERALS.keys.sort.reverse

# if the number is greater than half way, subtract from the larger numeral
# if the number is less than half way, then add to the smaller numeral

def roman(n, max=0)

  if numeral = BASIC_NUMERALS[n]
    numeral
  else
    i       = NUMERAL_VALUES.index { |val| n >= val }
    smaller = NUMERAL_VALUES[i]
    bigger  = NUMERAL_VALUES[i-1]

    # p smaller: smaller, bigger: bigger

    if n == bigger - 1
      roman(bigger - n, i) + roman(bigger)
    else
      roman(smaller, i) + roman(n - smaller, i)
    end

  end

end


# Bugs:
# - You can only subtract ONE number from another.
# - "Groups" of numerals (sets of numerals that end up being added together) must be ordered from largest to smallest.

(1..50).each do |n|
  puts "#{n}: #{roman(n)}"
end