Not the easiests of problems though. Do you know what statistics you would apply?

IQ measurements seem to have a similar problem: doing test a, influences your score on test b, because you get more used to the problems presented.. but doing test a and b just marginally increases your general intelligence, which is what you are trying to measure, while it might have a big influence on someone's score in these tests.

With IQ tests, you can expect that doing test c till z will eventually saturate someone.. but that might only work because you generally do not get the answers. In coding, you do get the answer back (whether your code compiles/works or not), so eventually both programmers will just be limited by the speed with which they type.