How can I convert a Firebase Database Snapshot into an Array List in Swift?

I am making an app using Swift and Firebase. I want to get an array list containing all of the numbers under a certain user id (images attached below). What I mean by this is I want to be able to call a function that returns an array list containing every integer (from low to high) placed as a child of the user id, but not containing their values (in this case "true"). I have already gotten a snapshot of the data (see code below), but I am unsure as to what to do now.

My Code:

func likeToLikeForAll() {

    let uid  = Auth.auth().currentUser?.uid
    Database.database().reference().child("Liked Movies").child(uid!).observeSingleEvent(of: .value, with: { (snapshot) in
        if let dictionary = snapshot.value as? [String: AnyObject] {
            print()
            print("SNAP:")
            print(snapshot.value!)
            print()
        }
    })
}

The function prints:

This is an image of the realtime database: