1) you are right, I and a lot of other guys are already doing this. 2) Indeed Cuda can be used with success, and this is probably the way to go. Unfortunately

1) you are right, I and a lot of other guys are already doing this. 2) Indeed Cuda can be used with success, and this is probably the way to go. Unfortunately I don't have any board at hand, but I'll buy one later in order to experiment with this technology. 3) This is not going to save you any time. Basically the part that alters the five chars at the end is nothing compared to the rest of the computation. There are other tricks that can be used, like to compute a fast hamming distance, just xor the bytes of the two strings and count the bits using a lookup table. Or even use some specific asm instruction for bit counting. But again unless you are doing this stuff of the xor in a very slow way this is a negligible amount of work: I commented out the hammer distance computation in my code and the numbers are exactly the smae, 3.5 million comparison per second per core more or less. Another obvious optimization is of course to avoid doing too much permutations of the words. For every permutation there are a lot of tries to do just altering the final five chars. Basically there is no way to win without to resort to fast hardware and parallelization, being it a large set of computers, CUDA, or a very lucky run that outputs in 30 hours an entry with an hamming distance of 31 or 32 just... against the probabilities ;) The only reason I'm running the contest is that it's funny and a very good way to teach something interesting to the programmers working in my company. We care a lot about having fun programming.