I highly recommend the book "Programming Challenges" by Steven Skiena, used in conjunction with UVA Online Judge at http://onlinejudge.org http://onlinejudge.or

I highly recommend the book "Programming Challenges" by Steven Skiena, used in conjunction with UVA Online Judge at http://onlinejudge.org http://onlinejudge.org. Each challenge takes the form of a word problem. The solution can be coded in a few different languages and uploaded to the website. The site imposes time limits when running the solution. When I've found that my solution works but is too slow, it has encouraged me to look for different data structures or algorithms. I can't recommend it enough.