Roman to Integer

来源：Leetcode

原帖：http://oj.leetcode.com/problems/roman-to-integer/

题目：
Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.

代码：

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