How do I prove to my professor that I didn't copy pasta another kid's work?

[COLOR="Red"]So, final project time for computer science. My buddy and I decided to work on it together as two minds would make the project work quicker and faster. Whenever we had to code, we coded separately, and compiled and ran it. Then, we saw how the other did what, and depending on who got it correct, we switched our codes to be more correct and functioning. Now, handing in the project, he states that our codes are too similar. I don't even know how to counteract his argument. Sure, parts of our code are similar, but that was to make the project work. Our formatting styles are vastly different. Mine is concise, to the point, and easily readable. His is messy, many non-needed lines of code, etc. He even decided to put in lines of code that would play a music file depending on how the code worked. I didn't. He had all these extraneous lines of code that clogged up the output. My output was really short. His sings and has smiley faces.

Thoughts? [/COLOR]