leetcode 13. 罗马数字转整数

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 ++)
        {  // 4xx, 9xx 特例，当前字母比后一个字母小，则-当前字母值， + 后一字母值
            if (i + 1 < s.size() && hash[s[i]] < hash[s[i + 1]])
                res -= hash[s[i]];
            else 
                res += hash[s[i]];
        }
        return res ;


    }
};