I was participating in a Facebook Midwest Regional Hackathon and was contacted by a recruiter shortly thereafter at my university.

We scheduled the first phone interview, which was technical. The questions included:

• Printing a binary search tree in reverse.
• Finding the k-th largest element in O(N) without modifying the node.
• Finding the k-th largest element in O(log N) time by keeping the size of the subtree in each node.

This is the "reverse" of the problem of finding the k-th smallest element in a tree. I had to find the k-th largest element.