1. Codewars
Codewars is where developers achieve code mastery through challenge. Train on kata in the dojo and reach your highest potential.
2. Exercism
Develop fluency in 55 programming languages with Exercism’s unique blend of learning, practice, and also mentoring. Exercism is really effective and also has an engaging UI.
3. CodeChef
CodeChef was created as a platform to help programmers make it big in the world of algorithms, computer programming, and programming contests.
4. HackerRank
The questions at HackerRank are typically puzzle-based, which can be good for people who are looking to advance their problem-solving skills or practice less traditional thinking.
5. Topcoder
Topcoder is home to the world’s largest community of designers, developers, and data scientists. Allowing you the freedom to start and execute faster.
6. LeetCode
LeetCode is the best platform to help you enhance your skills, expand your knowledge and prepare for technical interviews.
https://leetcode.com
7. Coderbyte
Challenge yourself to code and interview better. · Coderbyte is the platform where there are over a million developers who want to take their careers to the next level.
https://coderbyte.com
8. Project Euler
Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. This will help you become extremely good at problem-solving.
https://projecteuler.net
9. CodinGame
CodinGame is a challenge-based training platform for programmers where you can improve your coding skills with fun exercises (25+ languages supported)
10. SPOJ
Sphere Online Judge (SPOJ) is an online judge that provides over 20k coding challenges. You are able to submit your code to an online editor. SPOJ also hosts its own contests and has an area for users to discuss coding challenges.
https://spoj.com
