LeetCode 13. 罗马数字转整数

class Solution {
     
public:
    int romanToInt(string s) {
     
        unordered_map<char, int> hash;
        hash['I'] = 1, hash['V'] = 5;
        hash['X'] = 10, hash['L'] = 50;
        hash['C'] = 100, hash['D'] = 500;
        hash['M'] = 1000;

        int res = 0;
        for(int i = 0; i < s.size(); i ++){
     
            if(i + 1 < s.size() && hash[s[i]] < hash[s[i + 1]]) res -= hash[s[i]];
            else res += hash[s[i]];
        }

        return res;
        
    }
};