At a certain point, your resume should speak for itself. The fact that experienced engineers with impressive resumes are put through these types of interviews is insulting and frustrating to the interviewees. Succeeding at these whiteboard questions requires weeks of preparation. You need to practice, practice, practice. After enough practice, you are pretty likely to pass. So ultimately, it is more of a test of "how…
How do you practice answering whiteboard questions?
No computers. Pen only.
For me, rehearsing an answer works out. Then, I try to see how to deconstruct it and apply it to a similar problem I don't know.
I can deliver an answer sounding confident and competent because I practiced an answer. It's a bit of a crap shoot.
What irks me the most is that people are doing the interviews. They can be fooled and persuaded with tones and intonations without them realizing it.