Those would be useful optimizations once the simplest thing works. However the goal here is 500 lines- not fast, correct, maintainable code. If I was to write this for real world use I wouldn't start with C in the first place.

That's why I described a not very well known trick that requires just +1 line, the definition of hash(). It's neither fast nor maintainable, it's just a neat hack that gives you some of the performance of hash tables for negligible source code overhead. Perfect for tiny, self-contained programs like this one.