通过不断的定位基准数的位置来实现快速排序

<?php
/**
 * Created by PhpStorm.
 * User: saint
 * Date: 15/8/5
 * Time: 上午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) {
 
            // 从右向左查找比基准数小的单元
            while(($standard <= $this->a[$j]) && ($j > $i)) {
                $j--;
            }
 
            // 从左到右查找比基准数大的
            while(($standard >= $this->a[$i]) && ($j > $i)) {
                $i++;
            }
 
            $tmp = $this->a[$i];
            $this->a[$i] = $this->a[$j];
            $this->a[$j] = $tmp;
        }
 
        // 确定基准数的位置
        $this->a[$left] = $this->a[$i];
        $this->a[$i] = $standard;
 
        $this->qsort($left, $i - 1);
        $this->qsort($i + 1, $right);
    }
 
    // 执行函数
    public function main()
    {
        $left = 0;
        $right = count($this->a) - 1;
        $this->qsort($left, $right);
        print_r($this->a);
    }
}
 
$demo = new Demo();
$demo->main();

来自：http://my.oschina.net/liuke1556/blog/488215