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So several people replied with this same thing, which I have heard before being suggested. However, as I recall it at the time, if you tried to search for "invert binary tree" this term basically did not exist on the internet. I just tried searching on google with time set between 2000 and end of 2014 which seems to give similar results.

I guess I did not spell it out in my original post, but I always felt it might have been an intentional nonsense question intended to gauge how he would react to someone talking nonsense, or something like that, and not necessarily related to technical things. A sibling post of my original to suggest this was the case, without the weird detour through the term "invert binary tree".

Edit: Of course an alternative explanation is that the interview used another term and he then used the term "invert" on twitter.

Idk, this example at least has to me always felt like people who complain about not passing the driver's test coz they did some minor error and then forgetting to mention that they drove past a stop sign.

I haven't tested this myself, but from what I have heard it is not necessarily a good idea to store several different things in a single byte like this. While it may consume less memory there is a performance cost for each access since you may need to do masks and shifts.

Of course, there is a non-trivial performance trade-off with more cycles but more objects fits in cache, etc.

Some quick googling gave for example this source which seems to hint that under some situations it is not worth it at least https://stackoverflow.com/questions/4240974/when-is-it-worth...

Lastly, it seems like being quite harsh to call the code being of poor quality because of something like that. Unless it really is very important to get the extra memory, just the maintenance cost of packing things efficiently might make it not worth it. Even production code bases such as the JVM will happily use a single byte (or even more?) to store a boolean, and such things probably occur all over the place.

Was it ever figured out what "invert a binary tree" means? At least I had never heard this term used prior to this incident. This has me slightly worried about this particular example somehow, and I'm not quite sure what to make of it...