<font size =5 color=#22aa22>我现在在做一个叫《leetbook》的开源书项目，把解题思路都同步更新到github上了，需要的同学可以去看看
地址：https://github.com/hk029/leetcode
这个是书的地址：https://hk029.gitbooks.io/leetbook/
这里写图片描述
- Roman to Integer
问题
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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思路
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1,000 |
首先要知道罗马数字的规律：
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1,000 |
然后还有一个规则是，罗马数字从左自右相加，但是如果小数字A在大数字B之前，表示B-A
VI = 5+1 = 6
IV = 5-1 = 4
因此，利用2个变量保存当前数字和之前的数字就行了。因为这题很简单，用python比较方便，我就用python做的
class Solution(object):
def romanToInt(self, s):
sum=0
pre = 2000
cur = 0
Map = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000}
for i in range(len(s)):
cur = Map[s[i]]
sum = sum+Map[s[i]]
if cur > pre :
sum = sum-2*pre
pre = cur
return sum
