0013.cpp

class Solution {
  public:
    int value(char c) {
        switch (c) {
        case 'I': return 1;
        case 'V': return 5;
        case 'X': return 10;
        case 'L': return 50;
        case 'C': return 100;
        case 'D': return 500;
        case 'M': return 1000;
        default: return -10000;
        }
    }

    int romanToInt(string s) {
        int size = s.size();
        int res = 0;
        for (int i = 0; i < size - 1; i++) {
            int a = value(s[i]);
            int b = value(s[i + 1]);
            if (a >= b)
                res += a;
            else
                res -= a;
        }
        res += value(s[size - 1]);

        return res;
    }
};