12. Integer to Roman

• categories: Code, Interview Question, leetcode, Medium
• source: https://leetcode.com/problems/integer-to-roman
• topics: String Manipulation

Description

Seven different symbols represent Roman numerals with the following values:

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

Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules:

• If the value does not start with 4 or 9, select the symbol of the maximal value that can be subtracted from the input, append that symbol to the result, subtract its value, and convert the remainder to a Roman numeral.
• If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol, for example, 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD) and 900 (CM).
• Only powers of 10 (I, X, C, M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V), 50 (L), or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form.

Given an integer, convert it to a Roman numeral.

Idea

Hashtable and reversed iteration

Code

class Solution:
    def intToRoman(self, num: int) -> str:
        symbols = {
            1: 'I',
            4: 'IV', 
            5: 'V', 
            9: 'IX', 
            10: 'X', 
            40: 'XL', 
            50: 'L', 
            90: 'XC', 
            100: 'C', 
            400: 'CD', 
            500: 'D', 
            900: 'CM', 
            1000: 'M'}
 
        ans = ""
 
        for s, c in reversed(symbols.items()):
            while s <= num:
                ans += c
                num -= s
 
        return ans