source-code/Roman_to_Integer.cpp

class Solution {
public:
    int romanToInt(string s) {
        unordered_map<char, int> roman;
        roman['M'] = 1000;
        roman['D'] = 500;
        roman['C'] = 100;
        roman['L'] = 50;
        roman['X'] = 10;
        roman['V'] = 5;
        roman['I'] = 1;

        int res = 0;
        for (int i = 0; i < s.length() - 1; ++i) {
            if(roman[s[i]] < roman[s[i + 1]]) {
                res -= roman[s[i]];
            } else {
                res += roman[s[i]];   
            }
        }
        res += roman[s[s.length() - 1]];
        return res;
    }
};