로만의 정수 알고리즘입니다.

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, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven 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. Input is guaranteed to be within the range from 1 to 3999.

Example 1:

Input: "III"
Output: 3
Example 2:

Input: "IV"
Output: 4
Example 3:

Input: "IX"
Output: 9
Example 4:

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

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

접근법

규칙 1.

이전 인덱스 값 < 이후 인덱스 값 - 뺄셈

규칙 2.

이전 인덱스 값 >= 이후 인덱스 값 - 덧셈

풀이

// 심볼로 포멧 정의
symbols = {
    "I": 1,
    "V": 5,
    "X": 10,
    "L": 50,
    "C": 100,
    "D": 500,
    "M": 1000
};

var romanToInt = function(s) {
  	// 결과값 변수
    value = 0;
    for(let i = 0; i < s.length; i+=1){
      // 삼항연산자를 활용해서 규칙을 실현
        symbols[s[i]] < symbols[s[i+1]] ? value -= symbols[s[i]]: value += symbols[s[i]]
    }
    return value
};

반성

1. switch를 쓰기전에 심볼을 생각해보자