A recruiter contacted me a few months before I was set to graduate from university.

First, there was a non-technical phone screen where I was asked about my interests and future career plans. The next step was to complete an online coding challenge. After this, I had a technical phone interview with an engineer. They asked me a hard problem that I wasn't able to figure out in 45 minutes.

Had I passed that stage, the next and final step would have been an onsite interview. My feeling is that there is some element of luck involved in the technical phone screen. Based on the questions I've seen given to other interviewees, there's quite a bit of variance in the difficulty of questions asked.

I'd rather not give out the exact details, but my phone interview problem was a tricky one. It involved an array representation of a data structure.