13. Roman to Integer

---

Description

Roman numerals are represented by seven different symbols: , , , , , and .IVXLCDM

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000
For example,  is written as  in Roman numeral, just two ones added together. is written as , which is simply . The number is written as , which is .2II12XIIX + II27XXVIIXX + V + II

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not . Instead, the number four is written as . Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as . There are six instances where subtraction is used:IIIIIVIX

I can be placed before (5) and (10) to make 4 and 9. VX
X can be placed before (50) and (100) to make 40 and 90. LC
C can be placed before (500) and (1000) to make 400 and 900.DM
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 is a valid roman numeral in the range .s[1, 3999]

---

Code

package main 

import "fmt" 

func main() {
	var inp string 
	fmt.Scan(&inp)

	fmt.Println(romanToInt(inp))
}

func romanToInt(s string) int {
	romanMap := map[byte]int{
		'I': 1,
		'V': 5,
		'X': 10,
		'L': 50,
		'C': 100,
		'D': 500,
		'M': 1000,
	}

	output := 0 

	for i := 0; i < len(s); i++ {
		placed := false

		if i + 1 < len(s) {
			// I가 I + 1 보다 작다면 ...
			if romanMap[s[i + 1]] > romanMap[s[i]] {
				output += romanMap[s[i + 1]] - romanMap[s[i]]
				placed = true
				i++
			}
		}

		if !placed {
			output += romanMap[s[i]]
		}
	}

	return output 
}

시간 복잡도는 여전히 O(n)으로, 문자열의 길이에 비례하여 효율적으로 동작합니다.