I think you will really enjoy reading
The crest of the peacock, non-european roots of mathematics
by George Gheverghese Joseph
Penguin Books 2000 (new edition), 455 pages.
ISBN: 0-14-027778-1
It has nice examples of very logical, but completely different ways of performing calculations (have you ever multiplied 2x2 with Mayan numerals?) which range from the blatantly obvious (the Aztec representation of 5) to the bizarre (the way the Babylonians handled irrational numbers).
If your interviewee can handle these, it is likely that he or she can also manage complex algorithms.