I have a list of nine different websites
(see them below) that I visit every-single-day to keep my programming skills in shape. I have no preference whatsoever since they are all pretty much the same, some of them have better coding problems than others but nothing special.
However, during the last two months I have been using LeetCode and HackerRank more than the others because they are used I have been interviewing with a lot of medium and big sized companies, the big ones usually ask medium/hard questions from LeetCode while the medium sized companies prefer to filter people via HackerRank.
- https://leetcode.com/
- https://www.codeeval.com/
- https://www.hackerrank.com/
- https://www.hackerearth.com/
- https://www.interviewbit.com/
- https://www.codingame.com/
- https://www.codewars.com/
- https://open.kattis.com/
- https://codefights.com/