php数组排序和分割字符串

function sortStr($str){

    $ary = str_split($str);
    sort($ary);
    $len = count($ary);

    $arr = array();
    for($i=0; $i<$len; $i++){
        $n = ceil($i/2);
        $k = ($i % 2 == 0) ? $len-1-$n : $n-1;
        $arr[] = $ary[$k];
    }

    return $arr;
}

$str = '952164387';
print_r(sortStr($str));

// 输出结果

Array
(
    [0] => 9
    [1] => 1
    [2] => 8
    [3] => 2
    [4] => 7
    [5] => 3
    [6] => 6
    [7] => 4
    [8] => 5
)