I had two in person interviews back-to-back. The first one was with an engineer; he just asked me to talk to him about a project I was working on and the associated challenges, likes, and dislikes. Right after that we jumped into a coding question which I cannot say specifically due to an NDA agreement. Honestly, my solution was suboptimal however, I talked through various solutions and their advantages with him (which showed my understanding of the tradeoffs between space and time complexity). I also coded it on the whiteboard very cleanly, fast and without errors. The second interview was with a manager who asked me many behavioural questions and one simple class design question. This interview went really well. We had a great chat and I had great answers to the questions I was asked. 2 weeks later I got an email with the offer. I just want people to know that it is fine if you don't think of the most optimal solution especially for a problem whose optimal solution is very hard to code on the spot. As long as you show you are capable of engineering analysis and can code cleanly and fast you should be fine.