[Yacoby]

Maybe they are a bad interviewer?

In my view, if the answer involves a topological sort the interviewer should know how to solve it and be able to follow and find errors in the candidates code. If the interviewer, knowing the answer, cannot find any issues then surely the code is fine (for code written in an interview)

[ellenhp]

It's also possible that she hadn't seen the particular algorithm used before, or that she was having an off day or stressing about a meeting immediately after the interview, or that there were errors that she did see and she didn't want to say "yeah there are errors here" because doing so could affect the candidate's confidence in the interviews after hers. I could imagine any of these being true. Or she could just be a bad interviewer.

[shuger]

That is irrelevant. Asking someone to type non trivial code outside of IDE and then expecting it to compile and run without issues is lunacy. Even junior programmers know this. The interviewer in this story was either an amateur, an idiot or on power trip.

[xenocratus]

If you can't assess someone on their response then you're not interviewing them, you're just giving an exam by proxy. But that might very well be because the whole recruitment process is thoroughly stupid.