(Laravel Eloquent) Get posts of category and all nested subcategories

dav :

I would like to retrieve all posts of chosen category and all nested subcategories. I mean sth like this:

[id= 1]-Category 1
[id= 7]--Category 1.1
[id=12]---Category 1.1.1
[id=13]---Category 1.1.2
[id= 9]--Category 1.2
[id= 3]-Category 2

At first I tried to get recursively all IDs of chosen category and all nested subcategories and then retrieve posts with those categories IDs.

I wrote method getSubcategoriesIds($category) in controller which actually give me what I want but it returns array with duplicated ids. For instans, category 1 I get:

array:10 [
    0 => 1
    1 => 7
    2 => 1
    3 => 7
    4 => 12
    5 => 1
    6 => 7
    7 => 12
    8 => 13
    9 => 9
]

How can I improve the method to return IDs without duplicates? Or maybe there is better way to revive those posts?

Here are my files:

Model Category.php:

class Category extends Model {

    public function parent() {
        return $this->belongsTo('App\Category', 'parent_id');
    }

    public function children() {
        return $this->hasMany('App\Category', 'parent_id');
    }

    public function subcategories() {
        return $this->children()->with('subcategories');
    }

    public function parents() {
        return $this->parent()->with('parents');
    }

    public function posts(){
        return $this->hasMany('App\Post');
    }
}

PostController.php:

public function show($id)
{
    $ids =$this->getSubcategoriesIds(Category::with('subcategories')->where('id', $id)->first()));
    $posts = Post::whereIn('category_id', $ids)->get();
    return view('post.index', compact('posts'));
}

public function getSubcategoriesIds($category) {
    $array = [$category->id];
    if(count($category->subcategories) == 0) {
        return $array;
    } 
    else  {
        foreach ($category->subcategories as $subcategory) {
            array_push($array, $subcategory->id);
            if(count($subcategory->subcategories)){
                $array = array_merge($array, $this->getChildren($subcategory->subcategories, $array));
            }
        }
        return $array;
    }
}

public function getChildren($subcategories, $array) {
    foreach ($subcategories as $subcategory)  {
        array_push($array, $subcategory->id);
        if(count($subcategory->subcategories)){
            return $array = array_merge($array, $this->getChildren($subcategory->subcategories, $array));
        }
        return $array;
    }
}

dav :

I found problem in my recursive method. I shouldn't have passed $array to the recursive method getChildrenIds().

Here is my solution (with some refactoring):

    public function getCategoriesIds($category)
{
    if(!empty($category))
    {
        $array = array($category->id);
        if(count($category->subcategories) == 0) return $array;
        else return array_merge($array, $this->getChildrenIds($category->subcategories));
    } 
    else return null;
}

public function getChildrenIds($subcategories)
{
    $array = array();
    foreach ($subcategories as $subcategory)
    {
        array_push($array, $subcategory->id);
        if(count($subcategory->subcategories))
            $array = array_merge($array, $this->getChildrenIds($subcategory->subcategories));
    }
    return $array;
}

and now $this->getCategoriesIds(Category::with('subcategories')->where('id', 1)->first()); returns:

array:10 [
0 => 1
1 => 7
2 => 12
3 => 13
4 => 9
]