[LeetCode] 13. Roman to Integer (python3)

https://leetcode.com/problems/roman-to-integer/

Roman to Integer - LeetCode

 

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 1. My first answer

특별한 심볼들을 먼저 계산하고 string에서 삭제

그리고 나머지 string에서 일반적인 심볼들을 계산

class Solution:
    def romanToInt(self, s: str) -> int:
        special_symbol_map = {'IV':4, 'IX':9, 'XL':40, 'XC':90, 'CD':400, 'CM':900}
        symbol_map = {'I':1, 'V':5, 'X':10, 'L':50, 'C':100, 'D':500, 'M':1000 }
        
        result = 0
                
        for symbol in special_symbol_map.keys():
            if symbol in s:
                result += special_symbol_map[symbol]
                s = s.replace(symbol,'')
                
        for i in range(len(s)):
            result += symbol_map[s[i]]
                
        return result

 

Solution 2. My second answer

한 번에 탐색하면서 처리 할 수는 없을까 고민해서 개선

 

string 앞에서부터 차례대로 탐색.

그 다음 문자가 지금 문자보다 큰 숫자면 지금 문자를 뻄.(특수한 경우)

그 외의 경우에는 더함.

class Solution:
    def romanToInt(self, s: str) -> int:
        symbol_map = {'I':1, 'V':5, 'X':10, 'L':50, 'C':100, 'D':500, 'M':1000 }
        
        result = symbol_map[s[-1]]
        for i in range(len(s)-1):
            if symbol_map[s[i]] < symbol_map[s[i+1]]:
                result -= symbol_map[s[i]]
            else:
                result += symbol_map[s[i]]
        
        return result

 

https://github.com/junyeollee/CODINGTEST_PRACTICE/blob/main/leetcode/%5BLeetCode%5D%2013.%20Roman%20to%20Integer.ipynb

GitHub - junyeollee/CODINGTEST_PRACTICE