TO maximize your learning, only look at my 
solution to each part after you have gotten 
yours working.  

Then, if you want to either use my solution to one part as the starting 
point for your next part, or incorporate some of its ideas into your 
solution before beginning the next part, feel free to do so.

Before you  use my solution, you should understand it all.
Ask questions if anything in my solution is unclear to you.