[LeetCode] 13번 Roman to Integer

문제

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.

예제

Example 1:

Input: s = "III"
Output: 3

Example 2:

Input: s = "IV"
Output: 4

Example 3:

Input: s = "IX"
Output: 9

Example 4:

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

Example 5:

Input: s = "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

## 조건

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].

풀이과정

내 풀이

def calculate(s1:str, s2:str):
        ans = 0
        if s1 == "I":
            if s2 == "V" or s2 == "X":
                ans = -1
            else:
                ans = 1
        elif s1 == "V":
            ans = 5
        elif s1 == "X":
            if s2 == "L" or s2 == "C":
                ans = -10
            else:
                ans = 10
        elif s1 == "L":
            ans = 50
        elif s1 == "C":
            if s2 == "D" or s2 == "M":
                ans = -100
            else:
                ans = 100
        elif s1 == "D":
            ans = 500
        elif s1 == "M":
            ans = 1000
        return ans

class Solution:
    def romanToInt(self, s: str) -> int:
        n = len(s)
        ans = 0
        for i in range(n-1):
            ans += calculate(s[i], s[i+1])
        ans += calculate(s[-1], "P")   
        
        return ans
    

예외인 경우를 고려하여 계산하는 함수를 만든 뒤, For를 돌려서 진행하였다. 연속하는 2문자를 계산해야하므로 마지막값은 indexerror를 피하기 위해 따로 상관없는 스트링과 계산을 진행하였다.

다른 풀이

class Solution:
# @param {string} s
# @return {integer}
def romanToInt(self, s):
    roman = {'M': 1000,'D': 500 ,'C': 100,'L': 50,'X': 10,'V': 5,'I': 1}
    z = 0
    for i in range(0, len(s) - 1):
        if roman[s[i]] < roman[s[i+1]]:
            z -= roman[s[i]]
        else:
            z += roman[s[i]]
    return z + roman[s[-1]]

dict을 활용하여 로마문자에 숫자를 대입하였다. 그리고 for문을 활용하면서 연속하는 두 문자를 비교하고 값을 계산한다. 마지막 문자는 비교대상이 없으므로 리턴시 추가하여 리턴한다.