First round is the HR screening, ask basic questions about yourself, your background, why interested in SIG, etc.; Second round is the technical telephone interview, the interviewer was arranged according to your background and experience.

Talk about one or two projects that you are proud of.

Why do we use Hashtable? And what is its time complexity?

Talk about the binary search tree? What is its time complexity?

Since in general the time complexity of Hashtable is O(1), why do we still use binary search tree? Can you tell some occasions where we use BST instead of Hashtable?