This repository houses all of my solutions to various programming challenge sites. Can't guarantee that all examples will work out-of-the-box, but feel free to open issues.
From the Advent of Code about page:
Advent of Code is an Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like. People use them as a speed contest, interview prep, company training, university coursework, practice problems, or to challenge each other.
Codewars is a great site for ramping up your programming skills in a variety of languages (20 as of this commit and they're adding support for more). My profile is here.
Redditors who frequent r/dailyprogrammer post daily challenges ranging from easy to hard. All languages that the ideone API supports can be run to verify correctness, and even then, languages that ideone does not yet support are more than welcome.
Much like codewars, HackerRank is a site that provides challenges ranging from "Hello, World!" to AI and security. My profile is here.