I applied for a software engineer position by employer referral, and then a recruiter contacted me after a week to set up the phone screening interview schedule.

The interview question was: Given a tree where each node has a key value, compute the sum of key values of all the nodes in the sub-tree rooted at each tree node. One restriction on the problem was that each node has a pointer to its parent node, but not to its children.

I was asked to write code in a Google Doc.

As a PhD student seeking a research-oriented position, I expected the interviewer to ask some questions about my research work during the interview. However, he never cared about my research and only asked coding questions. Though the question itself was not tricky, I took some time to adjust myself to this unexpected situation.