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<?php
declare(strict_types=1);
namespace leetcode;
class SortArrayByParity
{
public static function sortArrayByParity(array $arr): array
if (empty($arr)) {
return [];
}
for ($i = 0, $j = 0, $n = count($arr); $j < $n; $j++) {
if ($arr[$j] % 2 === 0) {
$tmp = $arr[$i];
$arr[$i++] = $arr[$j];
$arr[$j] = $tmp;
return $arr;
public static function sortArrayByParity2(array $arr): array
$n = count($arr);
[$res, $start, $end] = [array_fill(0, $n, 0), 0, $n - 1];
for ($i = 0; $i < $n; $i++) {
if ($arr[$i] % 2 === 0) {
$res[$start++] = $arr[$i];
} else {
$res[$end--] = $arr[$i];
return $res;