php使用递归与迭代实现快速排序示例

/**
* 递归法实现的快速排序
* @param $seq
* @return array
*/
function quicksort($seq)
{
if (count($seq) > 1) {
$k = $seq[0];
$x = array();
$y = array();
$_size = count($seq); //do not use count($seq) in loop for.
for ($i = 1; $i < $_size; $i++) {
if ($seq[$i] <= $k) {
$x[] = $seq[$i];
} else {
$y[] = $seq[$i];
}
}
$x = quicksort($x);
$y = quicksort($y);
return array_merge($x, array($k), $y);
} else {
return $seq;
}
}

/**用迭代实现
* @param $seq
* @return array
*/
function quicksortX(&$seq)
{
$stack = array($seq);
$sort = array();
while ($stack) {
$arr = array_pop($stack);
if(count($arr) <= 1){
if (count($arr) == 1) {
$sort[] = &$arr[0];
}
continue;
}

$k = $arr[0];
$x = array();
$y = array();
$_size = count($arr);
for ($i = 1; $i < $_size; $i++) {
if ($arr[$i] <= $k) {
$x[] = &$arr[$i];
} else {
$y[] = &$arr[$i];
}
}
!empty($y) && array_push($stack, $y);
array_push($stack, array($arr[0]));
!empty($x) && array_push($stack, $x);
}
return $sort;
}
//$testArr = array(5545, 5, 6, 7675, 100, 9, 233, 566, 789, 456, 23, 55, 7, 4, 343, 564, 5, 45657, 8, 998, 9, 34, 34, 55, 6, 5, 6433, 67, 6, 6766, 4, 2, 42, 25634, 34343, 3, 3, 454, 4, 65, 6678, 57, 5455);
for($i=0;$i<20;$i++){
$testArr[]=mt_rand(0,10000);
}
//var_dump($testArr);
echo count($testArr).'
';
$start=microtime();
echo count(quicksort($testArr)).'
';
echo microtime()-$start.'
';
var_dump(quicksort($testArr));
echo '------------------------------------------------------------------------
';
echo count($testArr).'
';
$start=microtime();
echo count(quicksortX($testArr)).'
';
echo microtime()-$start.'
';
var_dump(quicksortX($testArr));