CodingBat is a free site of live coding problems to build coding skill in Java and Python. Going through many practice problem is a great way to solidify your understanding of how the code should work. The CodingBat problems are designed to have low overhead: short problem statements (like an exam), nothing to install, immediate feedback in the browser, and there's lots of them to build up those skills.
I just started solving the CodingBat Problems. If you think there is a better solution than the solution I provided, feel free to fork it, and modify it.