swift - Count number of mutual friends in Firebase

Question

I'm trying to pull the number of mutual friends that I have with any given userID. I first pulled all my friends from Firebase and then I pulled the userID's friends. I'm just not sure how to count the number of mutual friends from there. Please let me know if I'm going about it the wrong way.

func fetchMutualFriends(myID: String, userID: String) {

    let myID = Auth.auth().currentUser!.uid

    let postRef = self.databaseRef.child("friends").child(myID)

    postRef.observe(.value, with: { (snapshot) in
        for childSnapshot in snapshot.children {
              print(childSnapshot)

        }
    })
    let postRef1 = self.databaseRef.child("friends").child(friendID)

    postRef1.observe(.value, with: { (snapshot) in
        for childSnapshot in snapshot.children {
            print(childSnapshot)

        }
    })
}

Firebase structure

root/
|___ friends/
|      |___ myID
|              |___ friendID1
|      |___ friendID1
|              |___ myID

Answer 1

Waitting for answers