(LeetCode) Roman to Integer --- 罗马数字转整数

Given a roman numeral, convert it to an integer.

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

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解题分析：
首先要了解，罗马数字对应的整数：

"I":1, "V":5, "X":10, "L":50, "C":100, "D":500, "M":1000

然后要了解罗马数字的排序方式，从左到右依次从大到小。
# -*- coding:utf-8 -*-
__author__ = 'jiuzhang'
class Solution(object):
def romanToInt(self, s):
digits = { "I":1, "V":5, "X":10, "L":50, "C":100, "D":500, "M":1000 }
len_s = len(s)
num = 0
for i in range(0, len_s - 1):
cur = digits[s[i]]
next = digits[s[i + 1]]
if cur >= next:
num += cur
else:
num -= cur
num += digits[s[len_s - 1]]
return num