[mabbo]

I'd be more worried that in 3rd year of a CS undergrad you don't know how to implement data structures and algorithms.

1. There's lots of great books out there, and resources online. Learn what the interface of a given data structure is, and then go and try to implement it yourself in any way possible, then look up solutions for how it's typically done. Just code a lot! And learn what Big-O Notation is about, analyze your own solutions.

2. Both. It doesn't matter. Java is popular at Amazon, if that's your goal. Look, there's learning a programming language and there's learning to program, and these are different skills that complement each other. You will need to learn a new language a dozen times in your career, so just learn a few different ones right now and then focus on being a good programmer instead of a good C++ programmer.