roman_to_integer.js

/**
 * @param {string} s
 * @return {number}
 */
var romanToInt = function(s) {
    let sum = 0;

    let i = 0;

    while(i < s.length) {
        switch(s[i]) {
            case "I":
                if(s[i + 1] === "V" || (s[i + 1] === "X"))
                    sum -= 1;
                else
                    sum += 1;
                break;
            case "V":
                sum += 5;
                break;
            case "X":
                if(s[i + 1] === "L" || s[i + 1] === "C")
                    sum -= 10;
                else
                    sum += 10;
                break;
            case "L":
                sum += 50;
                break;
            case "C":
                if(s[i + 1] === "D" || s[i + 1] === "M")
                    sum -= 100;
                else
                    sum += 100;
                break;
            case "D":
                sum += 500;
                break;
            case "M":
                sum += 1000;
                break;
        }
        i++;
    }

    return sum;
};