[Hermitian909]

I wouldn't characterize it that way, I don't have a CS degree and could solve this trivially.

I think the question first asks the interviewee to have cracked an algorithms textbook or be clever enough to come up with the method on the spot.

Second, it asks if you can explain the concept to another engineer. I've met engineers in their 40s who can implement something like depth first search but cannot explain it. That's an immediate red flag to me that, at the very least, the person I'm talking to is not able to meet the responsibilities of a senior engineer.