[LeetCode]13. Roman to Integer - JavaScript

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👀 Problem

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 27is 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

var romanToInt = function(s) {
    const nums = {"I" : 1, "V" : 5, "X" : 10, "L" : 50, "C" : 100, "D" : 500, "M" : 1000};
    let ans = 0;
    
    for (let i = 0; i < s.length ; i++) {
        if(nums[s[i]] < nums[s[i+1]]) {
            ans -= nums[s[i]];
        } else ans += nums[s[i]];
    }
    return ans;
};

nums 객체에 로마자 문자열값을 key로 해당하는 숫자를 value로 저장한 후 s의 index 순서대로 key에 따른 value값을 더해주었다. 단 그 다음 문자가 앞문자보다 큰 값을 가지면 빼라는 의미이므로 if문을 통해 처리해주었다.