Roman to Integer

class Solution {
public:
    int romanToInt(string s) {
        int i =0;
        int next = 0;
        int res = 0;
        map<char,int> maproman;
        maproman.insert(pair<char, int>('I', 1));
        maproman.insert(pair<char, int>('V', 5));
        maproman.insert(pair<char, int>('X', 10));
        maproman.insert(pair<char, int>('L', 50));
        maproman.insert(pair<char, int>('C', 100));
        maproman.insert(pair<char, int>('D', 500));
        maproman.insert(pair<char, int>('M', 1000));
        while (i<s.length()){
            next = i + 1;
            if (next>=s.length()){
               return res +  maproman[s[i]];
            }
            else if (maproman[s[i]]>=maproman[s[next]]){
                res += maproman[s[i]];
                i++;
            }
            else{
                res += maproman[s[next]] - maproman[s[i]];
                i+=2;
            }
        }
        return res;
    }
};