quickSort.php

<?php

$a = array(1,2,5,9,8,7,4,5,6,5,8,15,10,25,85,4,1,2,78,9);

function qsort(array &$a, $low, $high)
{
    if ($low < $high){
        $pivot = partition($a, $low, $high);
        qsort($a, $low, $pivot - 1);
        qsort($a, $pivot + 1, $high);
    }
}

function partition(array &$a, $left, $right)
{
    $pivot = (int)($left + $right)/2;
    $pivVal = $a[$pivot];
    swap($a, $pivot, $right);
    $index = $left;
    for ($i = $left; $i < $right; $i++) {
        if ($a[$i] < $pivVal) {
            swap($a, $i, $index++);
        }
    }
    swap($a, $index, $right);
    return $index;
}

function swap(array &$a, $i, $j)
{
    $swap = $a[$i];
    $a[$i] = $a[$j];
    $a[$j] = $swap;
}

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