C - How to implement Set data structure?

Question

Is there any tricky way to implement a set data structure (a collection of unique values) in C? All elements in a set will be of the same type and there is a huge RAM memory

Answer 1

If the maximum number of elements in the set (the cardinality of the underlying data type) is small enough, you might want to consider using a plain old array of bits (or whatever you call them in your favourite language).

Then you have a simple set membership check: bit n is 1 if element n is in the set. You could even count 'ordinary' members from 1, and only make bit 0 equal to 1 if the set contains itself.

This approach will probably require some sort of other data structure (or function) to translate from the member data type to the position in the bit array (and back), but it makes basic set operations (union, intersection, membership test, difference, insertion, removal,compelment) very very easy. And it is only suitable for relatively small sets, you wouldn't want to use it for sets of 32-bit integers I don't suppose.