简单数组到关联数组，基于'目录树'，就像第一个数组的值一样

For example, I have array

Array
(
    [0] => folder1/file1.txt
    [1] => folder1/file2.txt
    [2] => file2.txt
    [3] => folder2/file1.txt
    [4] => folder1/subfolder1/file1.txt
    [5] => folder1/subfolder2/file2.txt
    [6] => file1.txt
    [7] => file3.txt
    [8] => folder1/subfolder2/file1.txt
)

I need a clue to figure how to create 'directory tree' array, based on the given values, that it could look like this:

Array
(
    [folder1] => Array
        (
            [0] => file1.txt
            [1] => file2.txt
            [subfolder1] => Array
                (
                    [0] => file1.txt
                )

            [subfolder2] => Array
                (
                    [0] => file1.txt
                    [1] => file2.txt
                )

        )

    [0] => file1.txt
    [1] => file2.txt
    [2] => file3.txt
)

Now second array is a tree of the first array (made manually). =)

And I can't figure how to achieve this automatically.

Simples example (demo), that will generate output like you wish, but you will get conflict if you will have same folder and file name in the same directory level (demo).

$files = [
    'folder1/file1.txt',
    'folder1/file2.txt',
    'file2.txt',
    'folder2/file1.txt',
    'folder1/subfolder1/file1.txt',
    'folder1/subfolder2/file2.txt',
    'file1.txt',
    'file3.txt',
    'folder1/subfolder2/file1.txt',
];

$tree = [];
foreach ($files as $file) {
    $a = explode('/', $file);
    $array = &$tree;
    foreach (array_slice($a, 0, -1) as $folder) {
        if (!isset($array[$folder])) $array[$folder] = [];
        $array = &$array[$folder];
    }
    $array[] = end($a);
}
print_r($tree);

To overcome problem with same folder and file named on the same level you can create folder indexes with slash at the end, like folder/, so there cannot be any conflict (demo).