13. 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 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].

 

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

 

풀이

40, 90 등 5의 배수에서 빼는 것은 큰 문자 앞에 작은 문자가 오는 것에서 착안하여, 문자열 맨 뒤부터 이전 문자보다 큰 값일 경우 더하고 작은 값일 경우 빼는 형태로 진행했다.

 

 

코드

class Solution {
    public int romanToInt(String s) {
        char[] chars = s.toCharArray();
    	int result = 0;
    	int prevNum = 0;
    	
    	for(int i = chars.length-1; i >= 0; i--) {
    		int curNum = charToInt(chars[i]);
    		if(curNum >= prevNum) {
    			result += curNum;
    		} else {
    			result -= curNum;
    		}
    		prevNum = curNum;
    	}
		
        return result;
    }

    public int charToInt(char c) {
		int res = 0;
		switch (c) {
			case 'M':
				res = 1000;
				break;
			case 'D':
				res = 500;
				break;
			case 'C':
				res = 100;
				break;
			case 'L':
				res = 50;
				break;
			case 'X':
				res = 10;
				break;
			case 'V':
				res = 5;
				break;
			case 'I':
				res = 1;
				break;
		}
		return res;
	}
}

 

 

결과

Runtime : 3 ms

Memory Usage : 44.84 MB