13. Roman to Integer

class Solution:
    def romanToInt(self, s):
        """
        :type s: str
        :rtype: int
        """
        res = 0

        dic = {}
        dic["M"] = 1000
        dic["D"] = 500
        dic["C"] = 100
        dic["L"] = 50
        dic["X"] = 10
        dic["V"] = 5
        dic["I"] = 1

        i = 0
        while i < len(s):

            s1 = dic[s[i]]

            if (i+1 < len(s)):
                s2 = dic[s[i+1]]

                if s1 >= s2:        # 如果s1 >= s2 说明是顺位，也就是说不是9 or 4
                    res = res + s1
                    i = i + 1
                else:               # 9 or 4
                    res = res + (s2 - s1)
                    i = i + 2
            else:
                res = res + s1
                i = i + 1
        return res