What does it mean to invert a binary tree? I'm not familiar with this operation on binary trees. Does it mean to swap parents with child nodes? Or to swap siblings?
Pretending you understand or blindly assuming what the interviewer meant is more of a red flag to me than requiring a few rounds of clarification.
In my opinion, an ideal interviewee would communicate that they don't fully understand the requirements and possibly offer a brief set of possible interpretations. Once the interviewer has clarified, my ideal interviewee would restate the clarification to demonstrate competence and verify their new interpretation of the requirements before proceeding.
If this was really about "reversing" the tree, as you mention, the question seems more likely to address how the candidate approaches the situation. Like, he should start by making sure they both agree on what the question actually means.
Once that's out of the way, it seems relatively easy to come up with a naive solution, without having memorised any algorithms. It seems more like a case of brainfreeze to me, which can be sort-of fixed with practice (which in turn many candidates refuse to do: the dreaded "If I have to cram for the interview, I don't want the job" statement.)
So maybe he really wasn't a good fit for Google, despite apparently being a rockstar developer. Hey, startups need rockstar devs too.
> Oddly enough, Google shows me interview questions where "inverting a binary tree" means something quite different — for example, flipping it upside down, and making the left leaf the root, the right leaf the left leaf and the root the right leaf.
Whaaaaa? I can't find this, but it seems like such a weird operation. Got a link?
The guy writing the tweet (not necessarily the interviewer).
https://wwwx.cs.unc.edu/~duozhao/entry/2014/12/binary-tree-u...
Although I do see this as something you could possibly do "for real". Sometimes you'd rather change your existing data once than continue carrying forward what amounts to hacks, which is what inverting the output would amount to. Reversing a binary tree would be what you'd run in a tool to migrate all of your data over from the old format to the new format.