LC 13. 罗马数字转整数

代码 :

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 ++ ) {
            // IV = - 1 + 5
            if(i + 1 < s.size() && hash[s[i]] < hash[s[i+1]]) {
                res -= hash[s[i]];
            }
            else {
                 res += hash[s[i]];
            }      
        }
        return res;
    }
};