I use Python (PyPy) to compete for global leaderboard positions.
The committed Python code is what I end up with after solving the 2nd part of each puzzle.
It's probably not pretty...
I also write some solutions in SWI Prolog 9.1 for fun (not for the leaderboard).
They are run from the command line like so:
swipl -O -t halt -g main 04.pl < 04.in