簡単なクイックソート

<?php
/**
 * Created by PhpStorm.
 * User: saint
 * Date: 15/8/5
 * Time:   11:49
 */
class Demo
{
    public $a = array(3, 6, 9, 2, 4, 7, 1, 5, 8, 0);

    public function qsort($left, $right)
    {
        if($left > $right) {
            return;
        }

        $i = $left;
        $j = $right;
        $standard = $this->a[$left];

        while($i != $j) {

            //               
            while(($standard <= $this->a[$j]) && ($j > $i)) {
                $j--;
            }

            //             
            while(($standard >= $this->a[$i]) && ($j > $i)) {
                $i++;
            }

            $tmp = $this->a[$i];
            $this->a[$i] = $this->a[$j];
            $this->a[$j] = $tmp;
        }

        //         
        $this->a[$left] = $this->a[$i];
        $this->a[$i] = $standard;

        $this->qsort($left, $i - 1);
        $this->qsort($i + 1, $right);
    }

    //     
    public function main()
    {
        $left = 0;
        $right = count($this->a) - 1;
        $this->qsort($left, $right);
        print_r($this->a);
    }
}

$demo = new Demo();
$demo->main();