# Roman to Integer Interview question asked by Top Companies

Suppose we have Roman literals; we have to convert them into an integer. As we know the Roman numerals represent in some different symbols as below:

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

## Solution in python3

```class Solution:
romman_to_number = {
"I": 1,
"V": 5,
"X": 10,
"L": 50,
"C": 100,
"D": 500,
"M": 1000
}

def romanToInt(self, s: str) -> int:
total = 0
for i in range(len(s)):
if i+1 < len(s) and self.romman_to_number[s[i]] < self.romman_to_number[s[i+1]]:
total -= self.romman_to_number[s[i]]
else:
total += self.romman_to_number[s[i]]