Roman To Int

let romanToInt = function(s) {
    if (!s) return 0;

    let mapping = {
        'I': 1,
        'V': 5,
        'X': 10,
        'L': 50,
        'C': 100,
        'D': 500,
        'M': 1000
    }

    let result = 0;
    for (let i = s.length - 1; i >= 0;) {
        if (mapping[s[i]] > mapping[s[i - 1]]) {
            result += mapping[s[i]] - mapping[s[i - 1]];
            i -= 2;
        }
        else {
            result += mapping[s[i]];
            i -= 1;
        }
    }

    return result;
}