https://www.codewars.com/kata/52724507b149fa120600031d

codewars.52724507b149fa120600031d.php

<?php

function number2words(int $number): string
{
    if ($number < 20) {
        return ones2words($number);
    } elseif ($number < 100) {
        return tens2words($number);
    } elseif ($number < 1000) {
        return hundreds2words($number);
    } elseif ($number < 1000000) {
        return thousands2words($number);
    }

    throw new OutOfRangeException();
}

function ones2words(int $number): string
{
    $ones = [
        0 => 'zero',
        1 => "one",
        2 => "two",
        3 => "three",
        4 => "four",
        5 => "five",
        6 => "six",
        7 => "seven",
        8 => "eight",
        9 => "nine",
        10 => "ten",
        11 => "eleven",
        12 => "twelve",
        13 => "thirteen",
        14 => "fourteen",
        15 => "fifteen",
        16 => "sixteen",
        17 => "seventeen",
        18 => "eighteen",
        19 => "nineteen"
    ];

    return $ones[$number] ?? '';
}

function tens2words(int $number): string
{
    $tens = [
        1 => "ten",
        2 => "twenty",
        3 => "thirty",
        4 => "forty",
        5 => "fifty",
        6 => "sixty",
        7 => "seventy",
        8 => "eighty",
        9 => "ninety"
    ];

    return implode('-', array_filter([
        $tens[floor($number / 10)] ?? '',
        ones2words($number % 10 ?: -1),
    ]));
}

function hundreds2words(int $number): string
{
    return implode(' ', array_filter([
        ones2words(floor($number / 100)),
        'hundred',
        number2words($number % 100 ?: -1),
    ]));
}

function thousands2words(int $number): string
{
    return implode(' ', array_filter([
        number2words(floor($number / 1000)),
        'thousand',
        number2words(floor($number % 1000) ?: -1),
    ]));
}