(13)Roman Number to Integer

class Solution {
public:
    int value(char ch)
    {
        if(ch=='I')
            return 1;
          if(ch=='V')
           return 5;
           if(ch=='X')
           return 10;
           if(ch=='L')
           return 50;
           if(ch=='C')
             return 100;
           if(ch=='D')
            return 500;
           if(ch=='M')
            return 1000;
           
           return -1;
    }
    int romanToInt(string s) 
    {
        int res=0;
        for(int i=0;i<s.length();i++)
        {
            int s1=value(s[i]);
            if(i+1<s.length())
            {
                int s2=value(s[i+1]);
                if(s1>=s2)
                {
                    res=res+s1;
                }
                else
                {
                    res=res+s2-s1;
                    i++;
                }
            }
            else
            {
                res=res+s1;
            }
        }
        return res;
    }
    
};