[13] Roman to Integer | Leetcode Easy

문제설명

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 one's 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.

결과예시

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.

제한사항

• 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].

파이썬 코드

class Solution:
    def romanToInt(self, s: str) -> int:
        m = 0
        res = 0
        romanTable = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
        
        roman = list(map(lambda x: romanTable[x], s[::-1]))
        for val in roman:
            m = max(m, val)
            if val < m:
                res -= val
            else:
                res += val
        
        return res

S[::-1]를 사용해서 문자를 거꾸로 읽고
map을 사용하여 한글자씩 romanTable에 있는 대치되는요소와 바꾼다.

반복문을 통해서 이전숫자보다 작으면 빼고 크면 더한다.