I have tried all of these out, and some have been very helpful. Always a good idea to test your knowledge (and update it as necessary)
List of Programming Challenge Websites
- https://www.topcoder.com/challenges
- https://www.hackerrank.com
- https://codefights.com
- https://www.codingame.com
- https://www.halite.io
- https://www.codewars.com
- https://projecteuler.net
- https://leetcode.com
- https://www.codechef.com
- https://www.hackerearth.com
- https://practity.com
- https://coderbyte.com
- https://www.codeabbey.com
- https://www.spoj.com
- https://codingbat.com
- https://dmoj.ca
- https://open.kattis.com
- https://exercism.io
- https://screeps.com
- http://rosalind.info
- https://reddit.com/r/dailyprogrammer
- https://www.geeksforgeeks.org
- https://codesignal.com
- https://perlweeklychallenge.org
- https://adventofcode.com
- https://www.dailycodingproblem.com
- http://www.4clojure.com
- https://www.thehuxley.com
- https://www.firecode.io
- https://edabit.com
- https://www.interviewbit.com/practice