13 Roman to Integer(罗马数字转int Easy)

题目意思：罗马数字转int

思路：字符串从最后一位开始读，IV：+5-1

 class Solution {
 public:
     int romanToInt(string s) {
         map<char,int> mymap;
         mymap['I']=;
         mymap['V']=;
         mymap['X']=;
         mymap['L']=;
         mymap['C']=;
         mymap['D']=;
         mymap['M']=;
         int ans=mymap[s[s.size()-]];
         for(int i=s.size()-;i>=;--i){
             if(mymap[s[i]]<mymap[s[i+]])
                 ans-=mymap[s[i]];
             else
                 ans+=mymap[s[i]];
         }
         return ans;
     }
 };