13. Roman to Integer

 1 class Solution {
 2 public:
 3     int romanToInt(string s) {
 4         if (s.size() == 0) return 0;
 5         map<char, int> m = {{‘I‘,1}, {‘X‘,10}, {‘C‘,100}, {‘M‘,1000}, {‘V‘,5}, {‘L‘,50}, {‘D‘,500}};
 6         int num = m[s[s.size() - 1]];
 7         for (size_t i = s.size() - 1; i > 0; -- i) {
 8             if (m[s[i]] > m[s[i - 1]]) num -= m[s[i-1]];
 9             else num += m[s[i-1]];
10         }
11         return num;
12     }
13 };