Was it necessary to know on the top of your head without Googling what a binary tree is for the position the candidate applied for?
I've been a developer for 12 years and I've never had the use for that. Computer science is a VERY large field and being good at everything is impossible.
Asking the right questions at interviews are crucial for finding the right people.
If a candidate for a programming job knows binary trees but doesn't listen to other peoples views I would say he's less worth to us than a listener that easily learns new concepts but is currently not familiar with binary trees.
BTW, leaving a candidate in tears is not professional recruiting. Please let someone with more people skills accompany you to your interviews, you might leave people with scars that takes years to heal.
I came across it when studying computer science 20 years ago, yes. Heard about it after that but never directly needed the knowledge.
I'm sure it's used under the hood in a lot of code I write and have written but so is XOR, manual memory management and a bunch of other lower level implementations that I don't need to spend time on when developing on a higher abstraction level.
Not sure why you would expect all programmers to know about binary trees specifically.
Binary trees are the simplest kind of nontrivial tree, and trees are used extensively in programming. Most computer problems are solved using trees of one kind or another.
If you've never needed to know it, what is its value for finding a good candidate? A lot of these questions are basically testing whether you did a CS degree. If you're self taught, you might be just as good a coder, but have never had reason to learn what a binary tree is or how to implement quicksort, or whatever similar puzzle.
It's a nice way to filter out people who can code and basically do the job, but didn't have the financial resources to get a CS education, and weren't lucky enough when researching to see that his is an interview question. Although at least they'll know for next time.
Asking the right questions at interviews are crucial for finding the right people. If a candidate for a programming job knows binary trees but doesn't listen to other peoples views I would say he's less worth to us than a listener that easily learns new concepts but is currently not familiar with binary trees.
BTW, leaving a candidate in tears is not professional recruiting. Please let someone with more people skills accompany you to your interviews, you might leave people with scars that takes years to heal.