Competitive programming is a hobby that I have dedicated a great deal of time to. If you are interested in problem solving, I strongly suggest you give competitive programming a try.
Here are some of my profiles on various competitive programming sites:
Over the course of my career, I have come across many beautiful problems. Here are some that I particularly enjoyed. The problems are in no particular order. List is a work in progress:
During high school, I also participated in the United States of America Computing Olympiad (USACO). I recommend high school students in the U.S. to participate in the monthly contests and socialize with the U.S. olympiad community (not just informatics) - there's a lot of great people you can meet!
I used to write on a blogspot for competitive programming: tonynater.blogspot.com. The blog has since been retired.
Back to other interests.