13. Roman to Integer

Given a roman numeral, convert it to an integer.

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

相比Interger to Roman，本题明显要简单一些，按照规则直接翻译就好。

AC代码：

class Solution(object):
    def romanToInt(self, s):
        roman_to_int = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
        i, num = 0, 0
        while i < len(s) - 1:
            if roman_to_int[s[i]] >= roman_to_int[s[i + 1]]:
                num += roman_to_int[s[i]]
            else:
                num -= roman_to_int[s[i]]
            i += 1
        num += roman_to_int[s[i]]
        return num