LeetCode 12. Integer to Roman

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

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

For example, 2 is written as II in Roman numeral, just two one’s added together. 12 is written as XII, which is simply X + II. The number 27 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.

Example 1:

Input: num = 3 Output: “III”

Example 2:

Input: num = 4 Output: “IV”

Example 3:

Input: num = 9 Output: “IX”

Example 4:

Input: num = 58 Output: “LVIII” Explanation: L = 50, V = 5, III = 3.

Example 5:

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

Constraints:

1 <= num <= 3999

c++ 解法

注意两次循环，控制 num 正好为零才算有解，从本质上 数字的表示是有唯一解的，所以这么循环一定能找到解。

class Solution {
public:
    string intToRoman(int num) {
        
        string res;
        string sym[] = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
        int val[] = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
        
        for(int i = 0; num !=0;i++)
        {
            while(num >= val[i])
            {
                num = num - val[i];
                res = res + sym[i];
            }
        }
        
        return res;
    }
};

python

def intToRoman1(self, num):
    values = [ 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 ]
    numerals = [ "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" ]
    res, i = "", 0
    while num:
        res += (num//values[i]) * numerals[i]
        num %= values[i]
        i += 1
    return res
    
def intToRoman(self, num):
    values = [ 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 ]
    numerals = [ "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" ]
    res = ""
    for i, v in enumerate(values):
        res += (num//v) * numerals[i]
        num %= v
    return res