Integer to Roman

From LeetCode

problem description / no solution provided

Solution in Python3

class Solution:
    def intToRoman(self, num):
        """
        :type num: int
        :rtype: str
        """
        val_sym = [
            (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")
        ]
        roman = ''
        for val, sym in val_sym:
            if num == 0:
                break
            n_sym = num // val
            roman += sym * n_sym
            num %= val
        return roman

I am lucky to get

Runtime: 112 ms, faster than 99.63% of Python3 online submissions for Integer to Roman.

Variants

Decimal digit

Iterate through decimal number num, map each digit, including 4 and 9, to roman numeral in many ways. Inspired by those approaches, we can also get our val_sym computed instead of hard-coded.

Replace certain pattern

We can ignore subtraction related rules while generating string roman, but dealt with those rules afterwards by replacing following patterns:

Replace	by
DCCCC	CM
CCCC	CD
⋮	⋮
VIIII	IX
IIII	IV