Possible to build a portfolio in a year?

I am debating whether to go to university this year for Compsci, or take a gap year. Primarily because I am not super into it, but it will expose me to a number of possible careers etc. However I really want to do 2D/3D Art degree, but I need to put together a half decent portfolio because I don't take any Art related A-levels.

I was wondering if it would be a good idea, to take a gap year, get a part time job and put together a good enough portfolio for entry into university next year, considering you need to show character concepts, environments, game assets, etc.

Alternatively would it be possible to do a Compsci degree and work on/build a good portfolio over the time I am at Uni? or complete the degree and educate myself outside of school for the skills I would need?

Advice would be great, Cheers!