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

def to_roman(num)
    Symbols.reduce "" do |memo, (divisor, letter)|
        div, num = num.divmod(divisor)
        memo + letter * div
    end
end