kyu4_roman_numerals_helper.py

"""
Write two functions that convert a roman numeral to and from an integer value. Multiple roman numeral values will
be tested for each function;

Modern Roman numerals are written by expressing each digit separately starting with the left most digit and skipping
any digit with a value of zero. In Roman numerals 1990 is rendered: 1000=M, 900=CM, 90=XC; resulting in MCMXC. 2008
is written as 2000=MM, 8=VIII; or MMVIII. 1666 uses each Roman symbol in descending order: MDCLXVI;

Input range : 1 <= n < 4000

In this kata 4 should be represented as IV, NOT as IIII (the "watchmaker's four");

Examples:
    to roman:
        2000 -> "MM"
        1666 -> "MDCLXVI"
        1000 -> "M"
        400 -> "CD"
        90 -> "XC"
        40 -> "XL"
        1 -> "I"
    
    from roman:
        "MM"      -> 2000
        "MDCLXVI" -> 1666
        "M"       -> 1000
        "CD"      -> 400
        "XC"      -> 90
        "XL"      -> 40
        "I"       -> 1

Help
    Symbol	Value
    I	1
    IV	4
    V	5
    X	10
    L	50
    C	100
    D	500
    M	1000

https://www.codewars.com/kata/51b66044bce5799a7f000003

"""


# arabic to roman numerals mapping;
ARABIC_TO_ROMAN = {2000: 'MM', 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 to arabic numerals mapping;
ROMAN_TO_ARABIC = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100,
                   'D': 500, 'M': 1000, 'MM': 2000}


class RomanNumerals:
    
    @staticmethod
    def to_roman(val : int) -> str:
        def __convert_to_roman(val, roman_numeral=''):
            while val > 0:
                for key, value in ARABIC_TO_ROMAN.items():
                    while val >= key:
                        roman_numeral += value
                        val -= key
            return roman_numeral
        
        return __convert_to_roman(val)

    @staticmethod
    def from_roman(roman_num : str) -> int:
        def __convert_to_arabic(roman_num):
            result, check = 0, 0
            
            for roman_numeral in roman_num:
                arabic_numeral = ROMAN_TO_ARABIC[roman_numeral]
                
                if arabic_numeral >= check:
                    result, check = result + arabic_numeral, arabic_numeral
                else:
                    result -= arabic_numeral
            
            return result
        
        return __convert_to_arabic(roman_num[::-1])