You may laugh at the utter simplicity of this test, but I administer this several times a week when I interview candidates.
I am still dismayed at how few programmers can solve this given 30 min (15 for the correct solution, plus 15 for optimizations across instructions and code brevity). It filters out the weak for sure.
Unfortunately it is really not, I have a friend who is just transitioning from junior to senior level and he is kind of coming to the realization that the majority of developers are really that bad. I usually look at elitist statements with a bit of septicemic because generally it is an average person trying to make themselves feel better, but in the case of the development world, it really is that bad. It is the reason that we have the 10x'ers.
For example a good developer should be able to solve this problem even if he has never used the technologies involved. It is that simple of a problem. I have never developed in Ruby in my life, 10 minutes on Google gave me all the Ruby API's I needed to complete the challenge. You see a good developer sees the solution and then figures out the API to do what they need it to do. Mastery of the technology is not what makes a good developer, seeing the solutions is where the value of a developer should be measured.
I am still dismayed at how few programmers can solve this given 30 min (15 for the correct solution, plus 15 for optimizations across instructions and code brevity). It filters out the weak for sure.