IntegerToRoman

Problem

https://leetcode.com/problems/integer-to-roman/

Solution

Observe that the Roman numeral for a number is composed of the Roman numerals for each digit. Suppose our digit is in the ones place. Then, the Roman numberal is ‘I’ repeated digit times if digit is less than 4 and ‘IV’ if digit is 4. For digit between 5 and 8, the Roman numeral is ‘V’ followed by ‘I’ digit - 5 times. Finally, if digit is 9, the Roman numeral is ‘IX’. For digits in the tens, hundreds, and thousands places, the pattern holds, but with different symbols for ones, fives, and tens.

Code

https://github.com/GeorgeRPu/tech-interview-prep/blob/main/solutions/IntegerToRoman.py

def intToRoman(num: int) -> str:
    """Convert an integer between 0 and 3999 to a Roman numeral.
    """
    thousands_digit = (num % 10000) // 1000
    hundreds_digit = (num % 1000) // 100
    tens_digit = (num % 100) // 10
    ones_digit = num % 10

    symbols = ['I', 'V', 'X', 'L', 'C', 'D', 'M', '?', '!']

    thousands_roman = roman_subnumeral(thousands_digit, *symbols[6:9])
    hundreds_roman = roman_subnumeral(hundreds_digit, *symbols[4:7])
    tens_roman = roman_subnumeral(tens_digit, *symbols[2:5])
    ones_roman = roman_subnumeral(ones_digit, *symbols[:3])

    return thousands_roman + hundreds_roman + tens_roman + ones_roman


def roman_subnumeral(digit, symbol, five_symbol, ten_symbol):
    """Generate the Roman sub-numberal for a single digit.
    """
    if digit < 4:
        return digit * symbol
    elif digit == 4:
        return symbol + five_symbol
    elif 5 <= digit < 9:
        return five_symbol + (digit - 5) * symbol
    elif digit == 9:
        return symbol + ten_symbol

Test

>>> from IntegerToRoman import intToRoman
>>> intToRoman(3)
'III'
>>> intToRoman(58)
'LVIII'
>>> intToRoman(1994)
'MCMXCIV'

Functions

`intToRoman`(num)	Convert an integer between 0 and 3999 to a Roman numeral.
`roman_subnumeral`(digit, symbol, five_symbol, ...)	Generate the Roman sub-numberal for a single digit.