Best places for training your brain and programming skills. Select one!

Hi steemians,
Are you train your brain in your free time?

I am goint to sokve some of them. I will be post my solution and I will be compare with your. And the best solution will be rewarded 💰

Please vote in comments for your preferred page. From page with most vote I will be solve examples.

Here is list of pages:

1. www.codewars.com - many algorithm and many programming languages

2. www.projecteuler.net - math examples

3. https://codecombat.com - The most engaging game for learning programming.

4. https://www.codingame.com - Learn new concepts by solving fun challenges in 25+ languages addressing all the hot programming topics

5. https://checkio.org - coding game where you build your space

Please select one.

thanks, have a nice day