Other programming challenge websites

Here is a list of some of our favorite challenge websites. Some of them are free, some are not. Some are math oriented, while others are more focused on pure programming. Some help with interview preparation, while others are just for fun.

Interview preparation:

• LeetCode: https://leetcode.com/
• HackerRank: https://www.hackerrank.com/
• CodeSignal: https://codesignal.com/
• Coderbyte: https://coderbyte.com/
• HackerEarth: https://www.hackerearth.com/

Competitive programming:

• Codeforces: https://codeforces.com/
• Topcoder: https://www.topcoder.com/
• AtCoder: https://atcoder.jp/
• Sphere Online Judge (SPOJ): https://www.spoj.com/

Skill building and learning:

• Project Euler: https://projecteuler.net/ (Fabrizio used to be a member of Project Euler’s dev team. He created some problems and collaborated on others)
• Exercism: https://exercism.org/
• Codewars...