Quick Sort

# Quick Sort

Zerethon Official Sample `quick-sort`, version 1.1.0, PHP 8.4.

- `quick_sort.php` — the algorithm, as shown in Zerethon Tools
- `main.php` — entry file: a short demonstration
- `test_quick_sort.php` — checks; set it as the entry file to run them

This project is your own copy. Changing it never changes the official sample.
See the algorithm animated: https://tools.zerethon.com/quick-sort-visualizer

<?php

require __DIR__ . '/quick_sort.php';

$a = [38, 27, 43, 3, 9, 82, 10, 27];
echo 'Before: [' . implode(', ', $a) . "]\n";
$result = $a;
quick_sort($result);
echo 'After:  [' . implode(', ', $result) . "]\n";
$expected = $a;
sort($expected);
echo 'Same as sort(): ' . ($result === $expected ? 'true' : 'false') . "\n";

<?php

// Quick Sort (Zerethon Official Sample: quick-sort 1.1.0).
// The algorithm as shown in Zerethon Tools.

function quick_sort(array &$a, int $lo = 0, ?int $hi = null): void {
    if ($hi === null) $hi = count($a) - 1;
    if ($lo >= $hi) return;
    $pivot = $a[$hi];
    $i = $lo;
    for ($j = $lo; $j < $hi; $j++) {
        if ($a[$j] < $pivot) {
            [$a[$i], $a[$j]] = [$a[$j], $a[$i]];
            $i++;
        }
    }
    [$a[$i], $a[$hi]] = [$a[$hi], $a[$i]];
    quick_sort($a, $lo, $i - 1);
    quick_sort($a, $i + 1, $hi);
}

<?php

// Checks for quick_sort. To run them, set this file as the entry file
// (the ▶ button next to it in Files) and press Run.

require __DIR__ . '/quick_sort.php';

/** Deterministic pseudo-random integers in [-50, 49] (the same as the Python checks). */
function numbers(int $seed, int $count): array
{
    $out = [];
    for ($i = 0; $i < $count; $i++) {
        $seed = ($seed * 1103515245 + 12345) % 2 ** 31;
        $out[] = $seed % 100 - 50;
    }

    return $out;
}

$cases = [[], [1], [2, 1], [1, 2, 3], [3, 2, 1], [5, 1, 5, 1, 5], [-3, 0, -1, 2]];
foreach ([[1, 10], [2, 50], [3, 200]] as [$seed, $size]) {
    $cases[] = numbers($seed, $size);
}

foreach ($cases as $a) {
    $result = $a;
    quick_sort($result);
    $expected = $a;
    sort($expected);
    if ($result !== $expected) {
        fwrite(STDERR, 'quick_sort([' . implode(', ', array_slice($a, 0, 6)) . "...]) is wrong\n");
        exit(1);
    }
}

echo 'All ' . count($cases) . " checks passed.\n";