What are /r/projecteuler's favorite Products & Services?

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It's about 100 milliseconds to answer both queries. If I removed the sorting call in the function and converted it into a loop instead of a recursion, I could probably shave off some of that time (and if I wrote it in C I could probably get it down to 1 millisecond or so), but it isn't really worth it :)

I'm currently extremely close to solving Problem 212, the combined volume of cuboids problem, which is a really, really tricky one. If I get it done, I'll post how I did it. My code is in C++ though, so it's quite long and I might just use pastebin or something. I have the algorithm down but there's a bug somewhere in the code that's giving me the wrong answer.

I recommend these books:

• Concrete Mathematics
• The Art and Craft of Problem Solving

The goal is to solve the problems in any way you can think of. Of course, bruteforcing might not be as fun as doing a better algorithm.

But there are a couple of problems which you HAVE to bruteforce. Take problem 27, for instance. Is there a non-bruteforce way to solve this?

Me too.

But DownForEveryoneOrJustMe keeps telling me it's "Just me."

Be good if there was a backup site where you could just check your answers.

I recommend reading Concrete Mathematics. Most of the material in that book is applicable to some project euler problems. Also The Art and Craft of Problem solving covers a lot of techniques that are essential for solving math problems. You can find older version of these books online.