This is Version 2.0 of Keith Pomakis' public domain Connect Four, platform independant algorithm.
When this AI is chosen, you are asked to pick a difficulty level from 1 to 10. The higher the number, the longer the computation takes. I wouldn't suggest levels 9 or 10 unless you are using a very slick machine such as a PowerMac.
The following is taken from his documentation:
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I developed this particular algorithm back in October 1992 for an Artificial Intelligence assignment. At the time, I implemented it in LISP. One year later I decided to convert the algorithm to C code so that I could use it as the smarts of a graphical front-end to the game. In performing the conversion, I took care to make the code as general as possible.
Version 2.0 was released in March 1995 when John Tromp (tromp@daisy.uwaterloo.ca) pointed out to me that I was only implementing "shallow" alpha-beta cutoffs and showed me how to implement "deep" cutoffs.
Thanks, John!
I am releasing these functions to the public domain. Therefore, people can use them, copy them, distribute them, modify them, and do whatever they want with them.
If you find any bugs (gasp!) or have any questions or comments about the functions or about the algorithm itself, you can contact me via e-mail. My address is "kppomaki@jeeves.uwaterloo.ca". I'd be interested in hearing what you think!
Oh, one other thing... I've put a lot of work into these functions, so I'd appreciate it if you kept my name attached to them when distributing or modifying them. If you actually use these functions for anything, give me credit somewhere!