Quick Sort

<?php
function sortQuick($a){ # a is an array of numbers

    # length of a
    $m = count($a);
    
    if($m < 2){
        return $a;
    }
    
    $pivot = $a[0];
    
    // declare two partitions
    $left = $right = array();
    
    for($i = 1; $i < $m; $i++){
        if($a[$i] < $pivot){
            $left[] = $a[$i];
        }
        else{
            $right[] = $a[$i];
        }
    }
    
    // use recursion to now sort the left and right lists
    return array_merge(sortQuick($left), array($pivot), sortQuick($right));
}

$arr = range(5, 0);
echo implode(', ', sortQuick($arr));

// 0, 1, 2, 3, 4, 5
?>