13. Roman to Integer C++

直接for循环，并且判断是否出现IV等情况

int which(char ch)
{
    if(ch == 'I')
        return 1;
    else if(ch == 'V')
        return 5;
    else if(ch == 'X')
        return 10;
    else if(ch == 'L')
        return 50;
    else if(ch == 'C')
        return 100;
    else if(ch == 'D')
        return 500;
    else return 1000;
}


class Solution {
public:
    int romanToInt(string s) {
        int flag = 0;
        int ans = 0;
        for(int i=0; i<s.size(); i++)
        {
            if(i != s.size()-1 && which(s.at(i)) < which(s.at(i+1)))
            {
                flag = 1;
            }
            if(flag)
            {
                ans -= which(s.at(i));
                flag = 0;
            }
            else
                ans += which(s.at(i));
        }
        cout << ans;
        return ans;
    }
};