I really appreciate your greater point. I've been given all sorts of CS problems in interviews that I don't have any background in understanding the context enough to know what to do. I changed careers from experimental physics, so my software work is essentially self taught. That doesn't mean I'm totally useless in my job or not an asset to my team or can't deliver products that generate massive revenue. But, those things are how interviewers make me feel.

Merging and comparing arrays as in that task also seems like something that might actually come up in a job.

However, I take the point of the other comment that the real issue here is doing it with certain speed requirements. That does make it harder, indeed, but still doable.

Self learning 'big O' is a waste of time and effort. Never have I needed to know it to accomplish a task beyond interviews. Don't nest six for loops, reading lines from a file into memory each loop. Got it, learnt it, can do. Next problem.

This gatekeeping attitude is bullshit.

Understanding Big O notation is not that difficult and everybody knows it is a common question in interviews. Analyzing specific algorithms can of course be difficult.

Having a CS degree gives you a large advantage when solving problems like this, but that advantage is markedly lower when you are trying solve typical real-world problems in the private sector.

Self-taught or not, no one is able to derive an optimal solution to algorithm problems on the fly. You must have previously learnt the technique, and probably practiced applying it a lot.