Leetcode: Roman to Integer

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

class Solution {
public:
    int romanToInt(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> nums;
        for(int i=0;i<s.length();i++){
            if(s[i]=='I') nums.push_back(1);
            else if(s[i]=='V') nums.push_back(5);
            else if(s[i]=='X') nums.push_back(10);
            else if(s[i]=='L') nums.push_back(50);
            else if(s[i]=='C') nums.push_back(100);
            else if(s[i]=='D') nums.push_back(500);
            else if(s[i]=='M') nums.push_back(1000);
        }
        int res=0;
        for(int i=0;i<nums.size();i++){
            if((i+1)<nums.size()&&nums[i]<nums[i+1]) res-=nums[i];
            else res+=nums[i];
        }
        return res;
    }
};