> For the complete documentation index, see [llms.txt](https://feifeizheng.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://feifeizheng.gitbook.io/leetcode/string/13.-roman-to-integer.md).

# 13. Roman to Integer

## Question

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, two is written as `II` in Roman numeral, just two one's added together. Twelve is written as, `XII`, which is simply `X` + `II`. The number twenty seven 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. Input is guaranteed to be within the range from 1 to 3999.

**Example 1:**

```
Input: "III"
Output: 3
```

**Example 2:**

```
Input: "IV"
Output: 4
```

**Example 3:**

```
Input: "IX"
Output: 9
```

**Example 4:**

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

**Example 5:**

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

## Code

```python
def romanToInt(self, s: str) -> int:
    roms = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
    res = 0
    for i, c in enumerate(s):
        #'IV' = 4, 'IX' = 9, subtract current val if next is larger
        if i+1 < len(s) and roms[s[i+1]] > roms[c]:
            res -= roms[c]
        else:
            res += roms[c]
    return res
```


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