I've had to work on tree traversal stuff multiple times in my life, anything low level GUI related will work with trees a ton.
I've also had to work with hash tables directly, and with memory caching layers.
I really should learn to write a proper parser, as I've had to write parsers multiple times now and they are always an ugly hack job.
I get that this is uncommon, but if you scratch beneath the surface, most software (browsers, databases, compilers, OSes) are full of this stuff.
Even while I was consulting stuff like this would come up. At one company we were using a custom graphql wrapper around a CMS, and it was missing some functions we needed. The wrapper was implemented like a compiler from the cms’s data format to a set of query functions. Fixing it to do what we needed it to do was really hard and broke my brain a bit. But I did it. And I wouldn’t have been able to without understanding compilers and algorithms.
You can spend your whole career walking the beaten path adding features to apps and websites, and never traversing a tree at all. There’s lots of work like that out there. But if you ever want to go deeper, you’ve gotta understand data structures and algorithms. I know not everyone is suited to it, and that’s fine. But there’s definitely a reason big tech asks about this stuff.
I don't think this is quite right. I think it's more like:
If you ever want to go deeper, you've gotta be able to recognize when the problem you're solving fits a pattern for which good data structures and/or algorithms exist, and you've gotta be able to find, understand, and apply good reference material.
Solving this "knowing what you don't know" problem is the best and most important role of formal education, in my opinion. It's not as important to know a topic as it is to know that it exists, and some of the basic terminology necessary to get started researching it further.
Nobody expects you to memorise a text book. But if an API gives you a list of items and you want to count the occurrences of each item, you should be able to figure out how to do that. And ideally in less than O(n^2) time if necessary. It’s surprising how many otherwise productive coworkers I’ve had who struggle with stuff like that.
Not now, when I'm just re-exporting ESM node packages as CJS so our legacy system can work with them
Graph search and B-trees I haven't done professionally since I left college though. But it is still good to know the theory when dealing with databases.
A lot of these algorithms is more about knowing their characteristics than knowing how to implement them. For example cryptographic algorithms can be complex, but having a good lib and knowing each crypto algorithm characteristics is usually good enough for almost everyone.
How many times did you have to write tree balancing code with no reference materials?
I've written AVL trees, B-trees, red black trees, and a bunch of other things people have named here. But, right now, without looking at any references, I couldn't even tell you how to balance an AVL tree, much less sit down and write out code for it.
Yes we've all done this in university. We've learned the theory. We had to write an implementation of this or that algorithm in whatever language the university made us use.
And we also know that great minds took a long time to come up with these in the first place. These "basic algorithms" are not something you think up in 5 minutes after first learning that computers exist or that some problem exists.
Bin packing algorithms are another such thing. Sure ask me interview "questions" like "please prove whether P=NP".
Eff off Mr. or Mrs. interviewer!
I do ask tree traversal questions when interviewing because I've had to traverse a lot of trees so I think being able to do an in order traversal of an already sorted binary tree (which is only a handful of lines of code) is fair game.
