I was first contacted by a recruiter, who scheduled me for a phone interview and an online skills assessment.

The phone interview took 20 minutes. I was called back within a few hours, and they informed me that they'd like to fly me down to headquarters for a day of interviewing.

I was then flown down three weeks later, where I spent the weekend in Redmond, WA, on an all-expenses-paid trip courtesy of Microsoft.

My day of interviews consisted of four one-on-one interviews with employees within a specific team. I was informed about a week later that they'd like to extend me an offer, which I gladly accepted.

Given an array of size N, filled with unique integers between 0 and N, how would you determine which integer was missing from the array?

This was an initially simple question that was made increasingly harder after each correct answer to incorporate such things as memory/processor limitations, etc.