12. Integer-to-Roman

/**
 * @param {number} num
 * @return {string}
 */
var intToRoman = function(num) {
    let res = [];
    const conversion = [
        [1, 'I'],
        [4, 'IV'],
        [5, 'V'],
        [9, 'IX'],
        [10, 'X'],
        [40, 'XL'],
        [50, 'L'],
        [90, 'XC'],
        [100, 'C'],
        [400, 'CD'],
        [500, 'D'],
        [900, 'CM'],
        [1000, 'M']
    ]
    for(let i = conversion.length - 1; i >= 0; i--){
        let [amt, key] = conversion[i];
        while(num >= amt){
            res.push(key)
            num -= amt;
        }
        if(num === 0)
            return res.join("");
    }
    return res.join("");
};