Codewars - Achieve code mastery through challenge.
LeetCode - Practice and level up your development skills and prepare for technical interviews.
Codility.com - The programmer testing solution that matches your job descriptions and helps you hire great...
HackerRank - HackerRank is a platform that allows companies to conduct interviews remotely to hire developers and for technical assessment purposes.
exercism - Download and solve practice problems in over 30 different languages.
Coderbyte - Coderbyte is a place built for anyone to practice and perfect their programming skills.