## 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, 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.
```

## Solutions

### 1. String

```
# Time: O(n)
# Space: O(n)
class Solution:
def romanToInt(self, s: str) -> int:
_dict = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000}
prev = 0
sum = 0
for i in s[::-1]:
curr = _dict[i]
if prev > curr:
sum -= curr
else:
sum += curr
prev = curr
return sum
# 3999/3999 cases passed (40 ms)
# Your runtime beats 88.02 % of python3 submissions
# Your memory usage beats 100 % of python3 submissions (12.7 MB)
```