I solved one of their puzzles and mailed them the answer, must be decade ago now. Did not even get an acknowledgement e-mail back.

I work at ITA and review puzzle submissions. I can't say what practices were 10 years ago (before we had our first customer!), but I would be shocked if this happened today or even several years ago when I joined. All of us did a puzzle to get an interview and we respect the time and effort it takes.

ITA probably had their first customer by the time, as it was already prominent and a success story in Lisp community. I must be misremembering the exact year.

Anyway, no biggie. The puzzle was among the simpler ones (solving a maze iirc), and I was mailing out tons of job applications at the time - with low expectations for each individual one.

And presumably instead of hiring you, they hired somebody just as capable but with a higher tolerance for solving boring problems for insufficient pay?

Sounds like a win-win.

I think these are good ideas to get a different view on candidates who love problems like these or see one that they are willing to do the problem set research about, but for this reason, should not be a "requirement" for candidates.