leetcode：Roman to Integer

class Solution {
public:
    int romanToInt(string s) {
         int map[128];
        if(s.size()==0)
            return 0;
        map[‘I‘]=1;
        map[‘V‘]=5;
        map[‘X‘]=10;
        map[‘L‘]=50;
        map[‘C‘]=100;
        map[‘D‘]=500;
        map[‘M‘]=1000;
        int res = map[s[0]];
        for(int i=1;i<s.size();i++)
        {
            if(map[s[i]]<=map[s[i-1]])
                res += map[s[i]];
            else
                res = res-2*map[s[i-1]]+map[s[i]];
        }
        return res;
    }
};