leetcode. 13 --- Roman numeral to integer

Roman numeral to integer

12 Turn the question upside down , Solve with hash table . Store Roman numerals and their corresponding values in a hash table , Traverse Roman numerals , If the Roman numeral of the current position is smaller than the one following it, you need to subtract the current Roman numeral , Otherwise, add the current Roman numerals .

The code is as follows ：

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;
    }
};