Competitive Programming
From charlesreid1
Notes for various programming competitions.
Lists
See List of Programming Competitions for web links to the many many competitions out there.
See List of ICPC Challenges for a list of links to various ICPC challenges. (These problems are pretty consistently difficult/challenging.)
See List of Challenging Programming Problems for a list of particularly challenging programming problems I've come across.
Notes
See Strategies for a list of strategies, lessons learned, and experience from the battlefield.
See Mistakes for a list of mistakes I have made, or that are commonly made by others.