LeeCode-Roman to Integer

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

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