[apocalyptic0n3]

Not necessarily. There are a lot of really good, self-taught engineers out there who have never had to do that before and likely don't even know what "invert a binary tree" means.

In my experience, it's much better to give them a problem to solve and have them walk you through the thought process as they try to figure it out. Even if they fail to solve it, the actual process gives you insight into how they think and how they'll perform on the actual job.

Unless your job regularly involves inverting binary trees, that's not a great question because it's basically asking if you've encountered something before. If you have encountered it, you likely know one a half dozen ways to solve it and everyone will give you roughly the same answer. If you've never encountered it, then you just fail even if are a good fit for the job. It doesn't reveal anything except you know one specific thing. In most cases, engineering jobs are problem solving for unique instances that arise day-to-day; a good interview should reflect that day-to-day reality more.