<?php

/**
 * Factorial
 */
function factorial($number)
{
    static $i = 0;
    static $internalNumber = null;

    if ($internalNumber === null) {
        $internalNumber = $number;
    }

    $i++;

    if ($i < $internalNumber) {
        return factorial($number * ($internalNumber - $i));
    }

    $i = 0;
    $internalNumber = null;

    return $number;
}

echo PHP_EOL;
var_export(factorial(6)); // 720
echo PHP_EOL;


/**
 * Bubble sort
 */
$array = [3, 4, 5, 1, 2];

do {
    $continue = false;

    for ($i = 0; $i < count($array) -1; $i++) {
        if ($array[$i] > $array[$i + 1]) {
            $temp = $array[$i + 1];

            $array[$i + 1] = $array[$i];
            $array[$i] = $temp;

            $continue = true;
        }
    }
} while ($continue);

echo PHP_EOL;
echo implode(', ', $array); // 1, 2, 3, 4, 5
echo PHP_EOL;

/**
 * Bubble sort reversed (or stone sort)
 */
$array = [1, 2, 5, 4, 3];

do {
    $continue = false;

    for ($i = count($array) - 1; $i > 0; $i--) {
        if ($array[$i - 1] < $array[$i]) {
            $temp = $array[$i - 1];

            $array[$i - 1] = $array[$i];
            $array[$i] = $temp;

            $continue = true;
        }
    }
} while ($continue);

echo PHP_EOL;
echo implode(', ', $array); // 5, 4, 3, 2, 1
echo PHP_EOL;