Microsoft Software Engineer - Internship interview questions

On campus, 30 min long. First 5 min ask about resume. Next 20 min build a bst from a preorderly arranged integer array, write the code on a white board. When finished, interviewer took a photo of the white board. Last 5 min Q&A.

It took 30 minutes and the recruiter asked me to explain 1 project in my resume, and asked a question involving removing duplicates from an array. After I gave my answer he asked how to make it more efficient and the Big O notation for it.