We software types must be masochists. It took Rob Pike an hour in the comfort of his private office to write this piece of code. How is this _at all_ like a typical software interview?

There's a common question, "convert an RE into an NFA" (https://en.wikipedia.org/wiki/Thompson%27s_construction)

I have seen this one go by, which, from the perspective of someone who has been doing regex implementation for 14 years, more or less, is fairly amusing. It seems unfair, as someone aware of potential pitfalls of backtracking would presumably feel obligated to build a automata-based solution; someone aware also of the potential pitfalls of DFAs (failure to determinize quickly on some nasty patterns) might also feel obligated to build a Thompson or Glushkov NFA solution as well.

It's quite possible you might turn someone competent into a gibbering wreck (they are asking me to implement RE2 or Hyperscan in an hour!) :-)

I used to use this exact problem years ago when interviewing candidates at Google. At that time I thought it was a great question, but now I'm not that sure anymore if this approach to interviewing is the best way to assess candidates.