Project Euler is without a doubt the internet's best repository of computational problems. At present (9/3/20), I've solved 45 out of 723. Beat me!
Perhaps you'll want to work through another book. The Structure and Interpretation of Computer Programs by Abelson and Sussman is one of the best. The language is Lisp. (Hope you like parentheses! I got tired of them and switched over to Python.)
How to Design Programs by Felleisen, Findler, Flatt and Krishnamurthi is also great. Again the language is Lisp (specifically the Scheme dialect of Lisp).
I mean math that will be helpful to programmers.
Definitely spend time with Knuth's Concrete Mathematics. It's a classic.