Day 10, 13 Roman to Integer

Roman to Integer
Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.
---------------------------
first, setup a dictionary, then walk through the whole string
according to the Roman numeral rule, if str[i] < str[i+1], then str[i] should be negative
watch out for the end element of the string, it could be compared to an unknown  value.
 

class Solution {
public:
    int romanToInt(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        unordered_map<char,int> k;
        k['I'] = 1;
        k['V'] = 5;
        k['X'] = 10;
        k['L'] = 50;
        k['C'] = 100;
        k['D'] = 500;
        k['M'] = 1000;
        int sum=0;
        for (int i=0;i<s.length();i++) {
            int sign = 1;
            if (k[s[i]] < k[s[i+1]]) {
                sign = -1;  
            }
            sum = sum + k[s[i]] * sign;
        }
        return sum;
    }
};

Added on Sep-02-2014
Handled final char in string

class Solution {
public:
    unordered_map<char,int> populateMap() {
        unordered_map<char,int> dic;
        dic['I'] = 1;
        dic['V'] = 5;
        dic['X'] = 10;
        dic['L'] = 50;
        dic['C'] = 100;
        dic['D'] = 500;
        dic['M'] = 1000;
        dic['e'] = 0;
        
        return dic;
    }

    int romanToInt(string s) {
        unordered_map<char,int> dic = populateMap();
        int ret = 0;
        s += 'e';
        
        for (int i = 0; i < s.length(); i++) {
            if (dic[s[i]] < dic[s[i + 1]]) {
                ret += dic[s[i + 1]] - dic[s[i]]; 
                i++;
            }else {
                ret += dic[s[i]];
            }    
        }
        return ret;
    }
};