这个选择排序代码有什么问题

 <?php
// Selection Sort in PHP
$arr = array(64, 25, 12, 22, 11);
var_export(selection_sort($arr));

function selection_sort($arr) {
    $len = count($arr);
    for($i = 0; $i < $len; $i++) {
        $min = $i;
        for($j = $i + 1; $j < $len; $j++) {
            if($arr[$j] < $arr[$min]) {
                $min = $j;
            }
            swap($min, $i, $arr);
        }
    }
    return $arr;
}

// pass by reference
function swap($i, $j, &$arr) {
    $tmp = $arr[$i];
    $arr[$i] = $arr[$j];
    $arr[$j] = $arr[$tmp];
}
?>

I get this error

PHP Notice: Undefined offset: 25 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined offset: 25 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined offset: 12 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined offset: 12 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined offset: 22 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined offset: 22 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined offset: 11 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined offset: 11 in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 PHP Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23

Notice: Undefined index: in /private/var/folders/83/98g8707d0f364z7m1pm76vlh0000gr/T/CodeRunner/Untitled 3.php on line 23 NULL

EDIT: NM got it By mistake I was using $tmp as index of an array instead of a value.

<?php
// Selection Sort in PHP
$arr = array(64, 25, 12, 22, 11);
var_export(selection_sort($arr));

function selection_sort($arr) {
    $len = count($arr);
    for($i = 0; $i < $len; $i++) {
        $min = $i;
        for($j = $i + 1; $j < $len; $j++) {
            if($arr[$j] < $arr[$min]) {
                $min = $j;
            }
            swap($min, $i, $arr);
        }
    }
}

// pass by reference
function swap($i, $j, &$arr) {
    $tmp = $arr[$i];
    $arr[$i] = $arr[$j];
    $arr[$j] = $tmp;
}
?>

change $arr[$tmp] to $tmp as $tmp has been the value while not the key.