With repeated practice, code challenge websites are a great way to become a more skillful and versatile programmer. Many teach advanced concepts like data structures and algorithms. They are also useful for preparing for interviews and showing off your skills to potential employers.
Here are some of my favorites:
CodeSignal — 450+ challenges that you can take in your preferred language. A nice UI makes this a pleasure to use.
Coderbyte — Exercises, user solutions, and interview prep courses at top tech companies.
Edabit — 4,500+ coding challenges. This is an approachable platform for coders of all skill levels.
Scotch.io — A monthly email with coding challenges. Each challenge includes resources, community discussion, and a solution posted the next week.
LeetCode — A polished platform with exercises and real interview questions from top tech companies.
HackerRank — Solve challenges in various programming and query languages. You can also solve company-sponsored challenges to apply for their jobs.
Exercism.io — A code practice and mentorship platform. They have 3000+ exercises across 50 languages. Unlike other platforms, these challenges are downloaded and completed locally.
Code Wars — Codewars has a serious collection of challenges that are submitted by their own community. These drills (called Kata) are accompanied by discussions and the ability to see the best solutions.
Challenge Rocket — A platform with hackathons and code challenges. Top performers are prospects to be hired by tech companies or win prizes.
Binary Search — Learn algorithms by solving problems together with others. Free forever.
AlgoExpert — A paid coding interview prep service with 85 hand-picked questions, hours of video explanations, data structures, and interview tips.
Repl.it Classroom — Repl.it is an online IDE. Their open-source classroom has code workouts in many programming languages.
CodeAbbey — CodeAbbey is the church for believers in repeated coding practice. By completing tasks you can become a Priest, Bishop, or even a Cardinal of code.
CodeChef — CodeChef is a platform to help programmers make it big in the world of algorithms and computer programming. They hold monthly contests and have a wide selection of puzzles.