If you are talking about think-cell: about 1.5 years ago, I applied, but was rejected after the programming test (even though they liked my CV and had to admit that the C++ code that I sent in was of decent quality).

Let me put it this way: I am more of a deep thinker than a fast thinker and (to put it in mathematical terms) more of a theory maker than a problem solver (i.e. I prefer Alexander Grothendieck over Paul Erdős, even though, of course, both were great mathematicians).

So, I was not capable to solve the hard algorithmic problem that think-cell had in their programming test in the given 9 hours; not for a lack of C++ skills, but for a lack of experience in developing "crazy" data structures and rather being a deep thinker/theory maker instead of a fast thinker/problem solver.