[Solved] Multiple Array puzzle

using combination of array_map, array_column and array_reverse :

$myArrays = array(
    array(1, 2, 3, 4),
    array(5, 6, 7, 8),
    array(9, 10, 11, 12),
    array(13, 14, 15, 16)
);

$index = 0;
$myArrays = array_map(function ($v) use (&$index, $myArrays) {
    if (($index % 2) != 0) {
        echo implode("\n", array_reverse(array_column($myArrays, $index))) . "\n";
    } else {
        echo implode("\n", array_column($myArrays, $index)) . "\n";
    }

    $index++;
}, $myArrays);

live demo : https://3v4l.org/0m2jZ

using foreach instead of array_map

foreach ($myArrays as $index => $myArray) {
    if (($index % 2) != 0) {
        echo implode("\n", array_reverse(array_column($myArrays, $index))) . "\n";
    } else {
        echo implode("\n", array_column($myArrays, $index)) . "\n";
    }
}

live demo : https://3v4l.org/RNC9R

both will output the following :

1
5
9
13
14
10
6
2
3
7
11
15
16
12
8
4