# 13. Roman to Integer

#### Easy

***

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:**

<pre><code>Input: s = "III"
<strong>Output:
</strong> 3
<strong>Explanation:
</strong> III = 3.
</code></pre>

**Example 2:**

<pre><code>Input: s = "LVIII"
<strong>Output:
</strong> 58
<strong>Explanation:
</strong> L = 50, V= 5, III = 3.
</code></pre>

**Example 3:**

<pre><code>Input: s = "MCMXCIV"
<strong>Output:
</strong> 1994
<strong>Explanation:
</strong> M = 1000, CM = 900, XC = 90 and IV = 4.
</code></pre>

&#x20;

**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]`.

```python
class Solution:
    def romanToInt(self, s: str) -> int:
        mappings = {'I': 1,'II': 2, 'III': 3, 'IV': 4,'V': 5,'IX': 9,'X': 10,'XL': 40, 'L': 50,'XC': 90,'C': 100,'CD': 400, 'D': 500, 'CM': 900,'M': 1000}
        num = 0
        index = 0
        while index < len(s):
            if index + 1 < len(s):
                if s[index: index+2] in mappings:
                    num += mappings[s[index: index+2]]
                    index = index+2
                else:
                    num += mappings[s[index]]
                    index += 1
            else:
                num += mappings[s[index]]
                index += 1
        return num
```