# 0013. Roman to Integer

https://leetcode.com/problems/roman-to-integer

## Description

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 one's 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
```

**Example 2:**

```
**Input:** s = "IV"
**Output:** 4
```

**Example 3:**

```
**Input:** s = "IX"
**Output:** 9
```

**Example 4:**

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

**Example 5:**

```
**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]`.

## ac

```java
```
