I secured the interview through a referral from a teacher who was in contact with the recruiter. The teacher provided my contact information to the recruiter, and a few days later, I received an email to schedule the first Skype interview.

The question I mentioned was from this initial interview. I succeeded in that stage and was offered a second Skype interview, which I did not pass.

It was a pretty straightforward process, though.

There was a tree. I was supposed to make a double linked list from the tree using a preorder traversal.