quicksort(Jon Bently<Beautiful code>)

quicksort.php

<?php
error_reporting(E_ALL);
ini_set('display_errors', 'on');
 
function quicksort(&$a, $l, $r)
{
	if ($l >= $r) return;

	/**
	 * {a}. item($a[$l]) is the pivot;
	 * {b}. items($a[$l+1, $m]) are all less than the pivot($a[$l]);
	 * {c}. if the item($a[$i], from $a[$l+1] to $a[$r]) is less than pivot($a[$l]), swap $a[++$m] and $a[$i],
	 *     to make sure {b} is always true.
	 * {d}. last, swap $a[$l] and $a[$m], to make $a[$m] to be the pivot, and now:
	 *     items($a[$l, $m-1]) are all less than the pivot($a[$m]),
	 *     items($a[$m+1, $r]) are all greater than the pivot($a[$m]).
	 */
	$m = $l;
	for ($i = $l + 1; $i <= $r; $i++)
	{
		if ($a[$i] < $a[$l])
		{
			++$m;
			list($a[$m], $a[$i]) = array($a[$i], $a[$m]);
		}
	}

	list($a[$m], $a[$l]) = array($a[$l], $a[$m]);

	quicksort($a, $l, $m - 1);
	quicksort($a, $m + 1, $r);
}

$a = range(1, 10);
shuffle($a);

print_r($a);
quicksort($a, 0, count($a) - 1);
print_r($a);