There are some questions which are answered quite well by a nearly-identical question on another site (say, computer science's stack exchange, or math overflow). Should those questions get answers just pointing towards those other sites? Should those questions be closed? etc.
Post No Bulls answered this in a Comment, and I'm promoting it to an Answer of the Community Wiki persuasion:
Related: Closing questions as off topic if they have an answer on mathoverflow?. My personal preference is to write a more accessible version of the answer from the other site. For example, I tried this here, which made sense because the MO answer was too terse for the OP to digest. (Though it's not clear if the OP benefited: he did not revisit MSE after my answer.)