Nope, you'll get a lawsuit for discrimination if you explicitly test for IQ. That's why they do it implicitly. The scheme is very simple: hire people with the highest IQ, and since they have high IQ, they will figure at least something out.

It tests for multiple things, at its best: A basic work ethic to understand fundamental CS concepts. Sure maybe plenty of people can't write a binary search in two minutes unless they practice live coding a bit, but plenty of people do study, so it self selects for that type.

There are also people who, no matter what, could not live code simple tree traversals or bin search or something, and it filters on that.

Finally, there's a pattern matching aspect to it. Some of the best interview questions I got involved very simple algorithms, but it was obfuscated by the problem. So the 'trick' was to just think through the problem and ask questions. Not to have memorized something obscure.

Indeed, there are even SaaS companies that will set it all up for you! I recently went through rounds that had a pretty blatant basic IQ test. I pushed back many times but the recruiter insisted it was required. I eventually complied, but it felt weird. I worry now my IQ score is in some database forever attached to recruiter's candidate profiling systems.