[LeetCode] Medium - 12. Integer to Roman (G,M,A,F)

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Question
Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

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1. Symbol       Value  
2. I             1  
3. V             5  
4. X             10  
5. L             50  
6. C             100  
7. D             500  
8. M             1000  

For example, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

* I can be placed before V (5) and X (10) to make 4 and 9.
* X can be placed before L (50) and C (100) to make 40 and 90.
* C can be placed before D (500) and M (1000) to make 400 and 900.
* Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999.

Example 1:

Input: 3
Output: "III"

Example 2:

Input: 4
Output: "IV"

Example 3:

Input: 9
Output: "IX"

Example 4:

Input: 58
Output: "LVIII"
Explanation: L = 50, V = 5, III = 3.

Example 5:

Input: 1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

Solution

Naive

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1. class Solution:  
2.     def intToRoman(self, num: int) -> str:  
3.         def i2r(d, roman_digits=['I', 'V', 'X']):  
4.             if d < 4:  
5.                 return roman_digits[0] * d  
6.             elif d == 4:  
7.                 return roman_digits[0] + roman_digits[1]  
8.             elif d == 5:  
9.                 return roman_digits[1]  
10.             elif d <= 8:  
11.                 return roman_digits[1] + roman_digits[0] * (d - 5)  
12.             else:  
13.                 return roman_digits[0] + roman_digits[2]  
14.               
15.               
16.         roman_level_digits = [['I', 'V', 'X'], ['X', 'L', 'C'], ['C', 'D', 'M'], ['M', '-', '-']]  
17.         roman_num = ''  
18.         level = 0  
19.         while num > 0:  
20.             remainder = num % 10  
21.             roman_num = i2r(remainder, roman_level_digits[level]) + roman_num  
22.             num //= 10  
23.             level += 1  
24.               
25.         return roman_num  

Runtime: 44 ms, faster than 82.16% of Python3 online submissions for Integer to Roman.
Memory Usage: 13.9 MB, less than 6.15% of Python3 online submissions for Integer to Roman.

Golden (link)

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1. def intToRoman(self, num: int) -> str:  
2.     thousands = ["", "M", "MM", "MMM"]  
3.     hundreds = ["", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"]  
4.     tens = ["", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"]  
5.     ones = ["", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"]  
6.     return thousands[num // 1000] + hundreds[num % 1000 // 100] + tens[num % 100 // 10] + ones[num % 10]  

Runtime: 44 ms, faster than 82.16% of Python3 online submissions for Integer to Roman.
Memory Usage: 13 MB, less than 98.46% of Python3 online submissions for Integer to Roman.