###### tags: `Hash Table`, `Math`, `String`

# LeetCode 13.Roman to Integer
Roman numerals are represented by seven different symbols: ```I```, ```V```, ```X```, ```L```, ```C```, ```D``` and ```M```.

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, ```2``` is written as ```II``` in Roman numeral, just two ones added together. ```12``` is written as ```XII```, which is simply ```X + II```. The number ```27``` is written as ```XXVII```, which is ```XX + V + II```.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not ```IIII```. Instead, the number four is written as ```IV```. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as ```IX```. There are six instances where subtraction is used:

- ```I``` can be placed before ```V``` (5) and ```X``` (10) to make 4 and 9. 
- ```X```can be placed before ```L``` (50) and ```C``` (100) to make 40 and 90. 
- ```C``` can be placed before ```D``` (500) and ```M``` (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer.

>Example 1:

Input: s = "III"
Output: 3
Explanation: III = 3.

>Example 2:

Input: s = "LVIII"
Output: 58
Explanation: L = 50, V= 5, III = 3.

>Example 3:

Input: s = "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

### Constraints:
- $1 <= s.length <= 15$
- s contains only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M').
- It is guaranteed that ```s``` is a valid roman numeral in the range [1, 3999].
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### Idea:
>
### Solution:

Python:

class Solution:
    def romanToInt(self, s: str) -> int:
        twokey = ['IV','IX','XL','XC','CD','CM']
        key={'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000}
        splits=len(s)
        add=[]
        total =0
        for i in range(splits):
            if i < splits-1:
                if s[i:i+2] in twokey:
                    add.append(0)
                else:
                    add.append(1)
            else:
                add.append(1)

        for i in range(splits):
            m2=key[str(s[i])]
            mit=add[i]
            if mit==1:
                total=total+m2
            elif mit==0:
                total=total-m2
        return total

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