Mathematician's solution: the entries in Pascal's triangle are combinations (n-over-k), which can be calculated directly: n-over-k = n!/((n - k)!k!). (If you want to be even faster, use Stirling's approximation to the factorial.)
Yes, neatly circumventing all of the clever algorithmic complexity optimisation that the interviewer is apparently looking for, and making this an even worse interview question.
