<?php
 
function parse_paths_of_files($array)
{
    $result = array();
 
    foreach ($array as $item)
    {
        $parts = explode('/', $item);
        $current = &$result;
        for ($i = 1, $max = count($parts); $i < $max; $i++)
        {
            if (!isset($current[$parts[$i-1]]))
            {
                 $current[$parts[$i-1]] = array();
            }
            $current = &$current[$parts[$i-1]];
        }
        $current[] = $parts[$i-1];
    }
 
    return $result;
}
 
$test = array(
    "dir1/dir2/dir3/file.ext",
    "dir1/dir2/dir3/file2.ext",
    "dir1/dir2/dir3/file3.ext",
    "dir2/dir4/dir5/file.ext"
);
 
print_r(parse_paths_of_files($test));
 
?>

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