Leetcode 13. Roman To Integer

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


Solutions
The description includes the example of 27. If the values are written from left to right in descending order, simply adding each number one by one will give the result.

XXVII

10(X) + 10(X) + 5(V) + 1(I) + 1(I) = 27

LVIII

50(L) + 5(V) + 1(I) + 1(I) + 1(I) = 58

But numbers like 4 and 9 are represented as a single number using two Roman numerals.

IV = 4
IX = 9

class Solution {
public:
    int romanToInt(string s) {
        int res = 0;
        unordered_map<char, int> roman = {
            {'I', 1},
            {'V', 5},
            {'X', 10}, 
            {'L', 50},
            {'C', 100},
            {'D', 500},
            {'M', 1000}
        };

        for (int i = 0; i < s.size() - 1; i++) {
            if (roman[s[i]] < roman[s[i + 1]]) {
                res -= roman[s[i]];
            } else {
                res += roman[s[i]];
            }
        }

        return res + roman[s[s.size() - 1]];        
    }
};