全排列(PHP)

/**
 * 全排列结果集
 * @var array
 */
private $fullpermutationarr = [];

/**
 * 全排列
 * user: lindsay
 * date: 2018/9/6
 * time: 9:43
 * @param $arr
 * @param string $str
 */
public function fullpermutation($arr, $str = '')
{
    $cnt = count($arr);
    if ($cnt == 1) {
        array_push($this->fullpermutationarr, $str ? $str . ',' . $arr[0] : $arr[0]);
    } else {
        for ($i = 0; $i < count($arr); $i++) {
            $tmp = $arr[0];
            $arr[0] = $arr[$i];
            $arr[$i] = $tmp;
            $this->fullpermutation(array_slice($arr, 1), $str ? $str . ',' . $arr[0] : $arr[0]);
        }
    }
}

// 调用

$this->fullpermutation([1, 2, 3, 4]);

$result = $this->fullpermutationarr;