romanNumeralConverter.js

/*
 * https://www.freecodecamp.com/challenges/roman-numeral-converter
 * */

/**
 * My original solution.
 *
 * @param {integer} num Number to transform.
 * @returns {string} Roman numeral equivalent.
 */
function convertToRoman(num) {

    /*
     * Shamelessly, I got the idea for the reference arrays on the Github
     * solutions wiki.
     *
     * This one really stumped me.
     * */
    var decimalArrReference      = [
            1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1
        ],
        romanNumeralArrReference = [
            'M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V', 'IV', 'I'
        ];

    /*
     * Using Array.prototype.reduce() to iterate over the reference array
     * felt cleaner than using a for loop or a while loop to iterate over the decimalArrReference array.
     *
     * But just to make sure, I clocked the performance and was disappointed
     * that my favored reduce() clocked far slower. I'm not surprised, though.
     * */
    var romanizedNumberArr = decimalArrReference.reduce(function (accumulator, decNum, idx) {

        while (decNum <= num) {
            accumulator.push(romanNumeralArrReference[idx]);
            num -= decNum;
        }

        return accumulator;

    }, []);

    return romanizedNumberArr.join('');
}

convertToRoman(36);

/**
 * "Basic" Solution found on Github.
 *
 * Often the "basic" solutions tend to be the best.
 *
 * You can see the original solution at the provided link.
 * Hats off to the contributors there.
 *
 * @link https://github.com/FreeCodeCamp/FreeCodeCamp/wiki/Algorithm-Roman-Numeral-Converter
 * @param {integer} num Number to transform.
 * @returns {string} Roman numeral equivalent.
 */
var convertToRomanTwo = function (num) {

    var decimalValue = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1],
        romanNumeral = ['M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V', 'IV', 'I'],
        decLength    = decimalValue.length, // store length here so we don't have to recalculate it on every loop.
        idx          = 0;

    var romanized = '';

    /*
    * Loop over every value in decimalValue array.
    *
    * I tend to favor while loops over for loops because
    * they clock a bit faster.
    * */
    while (idx < decLength) {

        /*
        * Continue to add the corresponding
        * romanNumeral to the converted string
        * until the current decimalValue doesn't
        * fit into the num any more.
        * */
        while (decimalValue[idx] <= num) {

            /*
            * Concat the roman numeral to the converted string.
            * */
            romanized += romanNumeral[idx];

            /*
            * continue to reduce the num by the decimalValue
            * otherwise we'd get an infinite loop.
            * */
            num -= decimalValue[idx];
        }

        // Move onto the next value in decimalValue array.
        idx ++;
    }

    return romanized;
}

convertToRomanTwo(36);