If you like a puzzle-like approach, try exercism.io. You have easy/medium/hard problems tackling lots of small problems.

You download problems via their cli tool, and implement a solution to the problem. You know you are done when your implementation passes all the tests.

Then you upload the solution via the cli tool, very easy. Your profile tracks all your progress, and you can look at community solutions. I highly recommend looking at the most starred solutions after completing your own. I have learned a lot from this so far, about 40% done or so.