In the future, I obviously need to work on coming up with better algorithms for solving these kinds of problems, but I'll probably continue to try and use Go because it's nice to have that fallback to sheer speed when my algorithm isn't great.
I benchmarked the I/O improvement I was thinking about. It actually only resulted in an improvement of about 30%. Worthwhile, probably, but not as "dramatic" as I thought it would be. Mea culpa.
It was only an EXAMPLE. It might be irrelevant to this particular issue, but look at the context of my comment: it isn't irrelevant to the subject of learning to code more efficiently.
But I would still suggest that, within the context of programming competitions, a certain kind of "programming efficiency" is close to irrelevant. A sloppily coded solution that nevertheless implements the proper algorithm can be many orders of magnitude faster than an efficiently coded implementation of a slow algorithm. Programming contests are more about having the insight to implement an algorithm having low big O, not so much about efficient coding practices. This isn't to say that efficient coding practices aren't important generally, just that there are much more important things to focus on in programming competitions.