Based on my experience interviewing at 3 separate software companies, I think that's fair to say.

Looking at any shortage by the number of applicants or job-seekers assumes that the bulk of the applicants are qualified to do the work.

This is not even remotely true in practice. A large proportion (over 50%, honestly) of the developers I've interviewed in my life can't tell the difference between a tree and an array, much less apply them intelligently. The majority cannot articulate the performance and storage differences between arrays and hash tables. These are the most basic qualifications for writing code.

Without excluding this massive, massive pool of yahoos, I don't think the statistics here are ultimately that meaningful.

> These are the most basic qualifications for writing code.

That seems like a very strong assertion. I don't have formal CS/data structures training; I've read about all of these structures in the past but probably wouldn't be able to answer your questions about them to the level you seem to expect. (I could tell the difference between a tree and an array, because they look different, but frankly I have no idea where it would make sense to use a tree; they aren't offered as a native type in any of the languages I use day-to-day and I've never missed them. I know a bit about the difference between arrays and hash tables because it's one of the most common criticisms of PHP, but again; to the extent that I use PHP--and I avoid it like the plague--their implementation of "arrays" using hash tables has never once affected me. It is the least shitty part of that language.)

So anyway, I confess my ignorance. And I'm very open to learning more about the structures you're talking about (seriously). But I (and many of the programmers I know) have been successfully writing programs that work for people who want it (and gladly pay for it) for a relatively long time without meeting your most basic qualifications.

You're overestimating the level I expect.

When I say that someone can't tell the difference between an array and a tree, I really mean someone does not know what a tree is. The number of interviews I've conducted where the candidate has heard of trees before, but cannot articulate, even in a basic way, what they are, is depressing.

To be more clear, the basic level I'm expecting is "it's a way to store data, where one object has children objects, which in turn have children objects", or something along that theme. Really, if you articulate in some way that it's stuff pointing to other stuff, you're already further along than half the people I've interviewed.

A lot of people can't even get that far.

These questions aren't designed to defeat you, they're questions that have depth so that you can get some idea about the candidate's level of understanding of data structures. Once you get past "it's an object with children" we can go deeper - what is the complexity of fetching an object out of a tree? What of sorting? Disadvantages and advantages in application? Cycle detection? All of these are nice to haves - but the basic requirement is that you have to know what a tree is.

Cool, okay that sounds pretty reasonable. Although I've successfully interviewed candidates without even asking them about trees, and they turned out just fine. I think there is a general tendency (and I don't intend to make assumptions about your specific case) towards overestimating the level of computer science knowledge required to crank out operational code for 99% of programming jobs. I think it's important for teams to have that knowledge within them, but not necessarily replicated through every individual member. (I know, I know, "A players" and all that... but the best teams I've known or been a part of, in programming or otherwise, had a couple of A players and a lot of B's who had the potential to be A's.)

EDIT: I'm more distressed by the number of applicants I've come across who've never written an SQL query, or have no idea what a database schema should look like (never mind noSQL stuff). I generally prefer working with programmers who understand and appreciate big picture design principles over the ones who sweat the details (because in my experience the former are usually able to pick up details pretty quickly, while the latter are not always able to appreciate the big picture design decisions being made) but in bigger teams there is presumably room/requirement for both types.

How do you know SQL and not know what a tree is ? How about we ask a simple SQL design question that you can't answer without knowing about the datastructures : what operations does an index accelerate, and which are unaffected and why ... How do you answer that without using the word hashmap/hashtable ?

It is entirely possible to use a database without understanding its internals. Look, I'm not encouraging incompetence--not by a long shot--I'm just challenging the assertion that everyone who "writes code" (the words 'potatolicious used, which started this sub-thread) needs to have the same knowledge base.

I've worked with a lot of academics who write code for math and stats without any real computer science knowledge (including no more than a rudimentary understanding of the most basic data structures). I have a business mentor who makes millions of dollars with a piece of legacy web software he wrote himself--I'm certain he could tell you that certain fields are indexed in the DB because the SQL performs better that way, but I doubt he would use the word hashmap/hashtable at all and that doesn't undermine his credibility in my eyes one bit. I have friends who write embedded code all day but couldn't write an SQL query to save their life; that is obviously fine for what they do, and it doesn't make them any worse of a programmer.

My example in the parent comment was obviously relating to web programmers, where the necessity of being able to write a usable SQL query is of far greater importance than the ability to explain how the database is actually executing that query. All I'm saying is that if we are able to deflate our own self-importance just a little bit (and accept the idea that the role of an employer might also be to act as a mentor), suddenly the pool of qualified applicants becomes bigger.