I used to do interviews at Google, and most likely, the interview process just failed in this case. Typically a candidate will do 5 technical interviews, where the Google engineers can ask basically anything they want to (eg. invert a binary tree in this case) and score the candidate. If the candidate trips up on one of these interviews, that can be enough to reject them. The process will sometimes randomly reject qualified people.
Additionally, I think people have a mis-perception of the skills required to work at Google:
> writing incredibly complex, highly performant algorithms for say search indexing, machine learning, ai, etc...
...
> Google was looking for a Computer Scientist here, not just another developer
This is not really the case. The large majority of positions are for basically "just another developer" to maintain an internal Java tool, or some web UI, or whatever. They are complex in that they have many dependencies and often lots of legacy code, but not all to different from Microsoft, Apple, Facebook, or any company with a large code base. In my several years at Google, 0-5% of my time was spent coming up with complex algorithms.
Additionally, I think people have a mis-perception of the skills required to work at Google:
> writing incredibly complex, highly performant algorithms for say search indexing, machine learning, ai, etc...
...
> Google was looking for a Computer Scientist here, not just another developer
This is not really the case. The large majority of positions are for basically "just another developer" to maintain an internal Java tool, or some web UI, or whatever. They are complex in that they have many dependencies and often lots of legacy code, but not all to different from Microsoft, Apple, Facebook, or any company with a large code base. In my several years at Google, 0-5% of my time was spent coming up with complex algorithms.