HackerRank has a pretty good collection of multi-language challenges with a range of difficulties and problem domains to choose from: https://www.hackerrank.co

HackerRank has a pretty good collection of multi-language challenges with a range of difficulties and problem domains to choose from: https://www.hackerrank.com/ https://www.hackerrank.com/ There's also a competitive aspect to it if you're into that kind of thing, but I personally just use it as a casual learning/interview prep tool. Their functional programming collection has been especially invaluable for me for getting used to solving problems in a functional mindset.