LeetCode | 13. Roman to Integer

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

class Solution {
public:
    int romanToInt(string s)
    {
        int res = 0, len = s.length();
        map<char, int> hash;
        hash.insert(make_pair('I', 1));
        hash.insert(make_pair('V',5));
        hash.insert(make_pair('X',10));
        hash.insert(make_pair('L',50));
        hash.insert(make_pair('C',100));
        hash.insert(make_pair('D',500));
        hash.insert(make_pair('M',1000));

        map<char, int>::iterator it1, it2;
        res = hash[s[len-1]];
        for(int i=len-2;i>=0;i--)
        {
            it1 = hash.find(s[i]);
            it2 = hash.find(s[i+1]);
            if(it1->second < it2->second)
                res -= it1->second;
            else
                res += it1->second;
        }
        return res;
    }
};