Quick Sort In-place Implementation，quicksort

Quick Sort In-place Implementation，quicksort

在线运行PHP http://www.compileonline.com/execute_php_online.php

 1 php
 2 function swap( &$a, &$b )
 3 {
 4     $c = $a;
 5     $a = $b;
 6     $b = $c;
 7 }
 8 
 9 /**
10 * quick sort
11 * ascend
12 * in-place
13 */
14 function quick_sort( &$a )
15 {
16     $s = count( $a ); // size of a
17     if ( $s return