Eli Bendersky's website Some may find it inappropriate that I post solutions to Project Euler in this blog. I don't share this sentiment, however. Here's an excerpt from the PE FAQ:
I solved it by using a search engine, does that matter? That depends on your motivation for solving the problems. It probably means that you've missed out on some beautiful and hidden mathematics.
If anyone races through PE using solutions of others, what has he gained? Will others feel they've been robbed? Isn't this, at the core, just an issue of personal integrity?
Anyways, if anyone's determined to find solutions to PE online, it's easy. This Haskell Wiki, for instance, holds code for the first 200 solutions. And other resources can be easily found by Googling.
I'm posting hints for some selected problems because I feel like sharing these insights with the readers of my blog, and this is also a good way to compare solutions with friends. It's the same motivation I've used for posting the solutions to almost all SICP exercises online. For some reason no one objected to that, although solved SICP exercises can lead to students cheating in homework, while Project Euler is just a game.
So take it easy, and if you don't want to spoil the solving experience for yourself, just don't look at these posts! I've conveniently hidden all the real hints behind a Read More link, so it won't be accidentally caught in your eyesight.