I founded a meetup based on adding a few rules to Project Euler to make it competitive. It was a lot of fun! The basic idea was that you formed teams and had 90 minutes to solve as many problems as you could, where each problem was worth its problem number in points.
Project Euler problems supposedly increase in difficulty as the problem number increments, though we discovered that that’s not necessarily true - if you look at the “Solved By” column in the problems you can see that some problems have been solved by more or less people than that problem’s neighbors, and you can judge relative difficulty that way.
It might also add some signal around which Project Euler problems you’d want to tackle next.
Project Euler now has difficulties you can sort by.
Wow, nice feature addition! Glad to see it.
Friend of mine had the idea to add alcohol to the mix but competition was not a part of it. I think he called it something like Eulers and Beers. Working groups of three and each person brings three vessels of one kind of craft beer or fancy soda. Three beers is generally enough for social grease for a couple of hours but generally not enough to get drunk when there’s food served, too. It keeps from having leftovers, too. I’ve not yet tried to put it together but I’d like to eventually.