My notes for installing on Arch Linux. I didn't use the AUR package (https://aur.archlinux.org/packages/kattis-problemtools/) because it wants to use python2.
The only troublesome dependency is plastex, which is not in the official arch repositories. I installed it from the AUR using this PKGBUILD (https://aur.archlinux.org/packages/plastex/). After that, I made some small edits to the PKGBUILD (see my version here: https://gist.github.com/arknave/36b486b5bb9328e13d45e6a160e81652) and makepkg -si just worked 🎉