hacker.org

in="cqrb lryqna rb fjh, fjh qjamna cqjw axc cqracnnw. qnan, hxd wnena twxf qxf oja cx bqroc! xq kh cqn fjh, cqn jwbfna rb mnjmvjwblqnbc."; a=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz; for i in $(seq 1 25); do echo "$in" | tr ${a:0:26} ${a:$i:26}; done

using sed:
$ cat grammar.sed
:a
s/A/is/g
...
s/S/JKL/g
t a
$ echo S | sed -f grammar.sed

I used a shell script for submitting results, downloading the next level and extracting the parameters. The actual solving is done in single-threaded C. Total CPU time (shell+C) for all levels is 30s in a 2.0GHz Core2. Most levels were solved in under 10ms, longest single-level runtime was 6.49s for...