0273-integer-to-english-words.js

/**
 * Integer To English Words
 * Time Complexity: O(1)
 * Space Complexity: O(1)
 */
var numberToWords = function (initialNumber) {
    if (initialNumber === 0) {
        return 'Zero';
    }

    const singleDigitWords = ['', 'One', 'Two', 'Three', 'Four', 'Five', 'Six', 'Seven', 'Eight', 'Nine'];
    const teenWords = ['Ten', 'Eleven', 'Twelve', 'Thirteen', 'Fourteen', 'Fifteen', 'Sixteen', 'Seventeen', 'Eighteen', 'Nineteen'];
    const tensWords = ['', 'Ten', 'Twenty', 'Thirty', 'Forty', 'Fifty', 'Sixty', 'Seventy', 'Eighty', 'Ninety'];
    const magnitudeWords = ['', 'Thousand', 'Million', 'Billion'];

    const convertThreeDigits = (segmentValue) => {
        let segmentStringRepresentation = '';

        const hundredsAmount = Math.floor(segmentValue / 100);
        const twoDigitRemainder = segmentValue % 100;

        if (hundredsAmount > 0) {
            segmentStringRepresentation += singleDigitWords[hundredsAmount] + ' Hundred';
        }

        if (twoDigitRemainder > 0) {
            if (segmentStringRepresentation !== '') {
                segmentStringRepresentation += ' ';
            }
            if (twoDigitRemainder < 10) {
                segmentStringRepresentation += singleDigitWords[twoDigitRemainder];
            } else if (twoDigitRemainder < 20) {
                segmentStringRepresentation += teenWords[twoDigitRemainder - 10];
            } else {
                segmentStringRepresentation += tensWords[Math.floor(twoDigitRemainder / 10)];
                const unitNumber = twoDigitRemainder % 10;
                if (unitNumber > 0) {
                    segmentStringRepresentation += ' ' + singleDigitWords[unitNumber];
                }
            }
        }
        return segmentStringRepresentation;
    };

    let workingNumber = initialNumber;
    let magnitudePosition = 0;
    const constructedParts = [];

    while (workingNumber > 0) {
        const currentThreeDigits = workingNumber % 1000;
        if (currentThreeDigits > 0) {
            let localizedWords = convertThreeDigits(currentThreeDigits);
            if (magnitudePosition > 0) {
                localizedWords += ' ' + magnitudeWords[magnitudePosition];
            }
            constructedParts.unshift(localizedWords);
        }
        workingNumber = Math.floor(workingNumber / 1000);
        magnitudePosition++;
    }

    return constructedParts.join(' ').trim();
};