LeetCode 013 Roman to Integer

class Solution {
public:
    int romanToInt(string s) {
        int result=0;
        int size=s.length();
        if(size==0)return 0;
        map<char, int> rom2int={{'M',1000},{'D',500},{'C',100},{'L',50},{'X',10},{'V',5},{'I',1}};
        for(int i=0; i<size; i++){
            if(i!=size-1 && rom2int[s[i]]<rom2int[s[i+1]]){
                result+=(rom2int[s[i+1]]-rom2int[s[i]]);
                i++;
            }
            else result+=rom2int[s[i]];
        }
        return result;
    }
};