For anyone that is doing CS at Columbia University or considering CU, if you like these types of coding challenges, definitely look into Professor Ross's Programming and Problem Solving class. It was one of the best CS classes I took at Columbia.

Here is his website: http://www.cs.columbia.edu/~kar/teaching.html

Each semester consists of 4 different open ended programming problems like these. You work as a team to compete against other members of the class. There's no tests and each class is run as an open seminar where people talk about their strategy and implementation and consider the best approach to solving these problems.

This was my favorite from my year: http://www.cs.columbia.edu/~kar/4444f02/node18.html