This is (was?) an epic web site:
Currently, they're struggling with a security problem.
Years ago, I found the site and quickly reached Level 2 by solving a flood of easy problems.
Recently, a recruiter strongly suggested reviewing problems on Project Euler as preparation for a job interview.
It was fun! I restarted my quest for being a higher-level solver.
Then they took the solution checking (and score-keeping) features off-line.
So now I have to content myself with cleaning up my previous solutions to make them neat and readable and improve the performance in some areas.
I -- of course -- cannot share the answers. But, I can (and will) share some advice on how to organize your thinking as you tackle these kinds of algorithmically difficult problems.
My personal preference is to rewrite the entire thing in Django. It would probably take a month or two. Then migrate the data. That way I could use RST markup for the problems and the MathJax add-on that docutils uses to format math. But. That's just me.
I should probably take a weekend and brainstorm the functionality that I can recall and build a prototype. But I'm having too much fun solving the problems instead of solving the problem of presenting the problems.