转罗马数字

intToRoman.js

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

function intToRoman(num) {
    return [['X', 'V', 'I', 1], ['C', 'L', 'X', 10], ['M', 'D', 'C', 100], ['', '', 'M', 1000]]
        .reduceRight(function (ret, item, index) {
            let count = ~~(num / item[3]) % 10;
            if (!count) return ret;
            if (count % 5 == 4) return ret + item[2] + item[count > 5 ? 0 : 1];
            return ret + item[1].repeat(count >= 5 ? 1 : 0) + item[2].repeat(count % 5);
        }, '');
};

romanToInt.js

const charValueMapping = {
    M: 1000,
    D: 500,
    C: 100,
    L: 50,
    X: 10,
    V: 5,
    I: 1
};

function romanToInt(s) {
    let sum = 0;
    let len = s.length;
    for (let i = 0; i < len; i++) {
        if (i + 1 < len && charValueMapping[s[i]] < charValueMapping[s[i + 1]]) {
            sum += charValueMapping[s[i + 1]] - charValueMapping[s[i++]];
        }
        else {
            sum += charValueMapping[s[i]];
        }
    }
    return sum;
};