leetcode Roman to integer

題目：
Given a roman numeral, convert it to an integer.

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

要把羅馬數字轉換為整數， 羅馬數字自行百度

code:

class Solution
{
  public:
    int romanToInt(string s)
    {
       map Roman;
       Roman['I'] = 1;
       Roman['V'] = 5;
       Roman['X'] =10;
       Roman['L'] =50;
       Roman['C'] =100;
       Roman['D'] =500;
       Roman['M'] =1000;
       int i=s.length()-1;
       int res;
       while(i>=0)
       {
          if(i==s.length()-1)
          {
            res=Roman[s[i]];
            i--;
          }

          if(Roman[s[i]] >= Roman[s[i+1]])
            res=res+Roman[s[i]];
          else
            res=res-Roman[s[i]];
          i--;
       }

       return res;
   }
};