# 2022-06-20

## 13. 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 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:

``````Input: s = "III"
Output: 3
Explanation: III = 3.``````

Example 2:

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

Example 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

#### Approach #0

``````var (
m = map[byte]int{
'I': 1,
'V': 5,
'X': 10,
'L': 50,
'C': 100,
'D': 500,
'M': 1000,
}
)

func romanToInt(s string) (ans int) {
var last int
for i := len(s) - 1; i >= 0; i-- {
v := m[s[i]]
if v >= last {
ans += v
} else {
ans -= v
}
last = v
}
return
}``````

Last updated