php 快速排序

<?php
function quickSort(&$a)
{
    $n = count($a);
    quickSortInternally($a, 0, $n-1);
}
function quickSortInternally(&$a,$l,$r)
{
    if ($l >= $r) return;
    $q = partition($a, $l, $r);
    quickSortInternally($a, $l, $q-1);
    quickSortInternally($a, $q+1, $r);
}
function partition(&$a,$l,$r)
{
    $pivot = $a[$r];
    $i = $l;
    for ($j = $l; $j < $r; ++$j) {
        if ($a[$j] < $pivot) {
            $temp = $a[$i];
            $a[$i] = $a[$j];
            $a[$j] = $temp;
            ++$i;
        }
    }
    $temp = $a[$i];
    $a[$i] = $a[$r];
    $a[$r] = $temp;
    return $i;
}
$a1 = [1,4,6,2,3,5,4];
$a2 = [2, 2, 2, 2];
$a3 = [4, 3, 2, 1];
$a4 = [5, -1, 9, 3, 7, 8, 3, -2, 9];
quickSort($a1);
print_r($a1);
quickSort($a2);
print_r($a2);
quickSort($a3);
print_r($a3);
quickSort($a4);
print_r($a4);

//打印数据如下：

//$a1:

Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 4
[5] => 5
[6] => 6
)

//$a2:
Array
(
[0] => 2
[1] => 2
[2] => 2
[3] => 2
)

//$a3:
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
)

//$a4:
Array
(
[0] => -2
[1] => -1
[2] => 3
[3] => 3
[4] => 5
[5] => 7
[6] => 8
[7] => 9
[8] => 9
)