Symmetric Difference of Two Arrays

Question

I have two NSArrays of Movie objects called DVD and VHS. I'd like to find the symmetric difference of these arrays. I want to know which Movies are in VHS buy not in DVD, and which Movies are in DVD but not VHS.

Can anyone tell me if there is a fast algorithm to solve it (preferably in C or Objective-C)? Is it faster/easier to solve if I use Dictionaries? What this kind of problem called (or is it just "Symmetric Difference")?

Thanks.

Answer 1

If you need VHS minus DVD, and DVD minus VHS in two different arrays, use -removeObjectsInArray:.

If you need them both in the same array, sort them and try to re-implement this algorithm in ObjC.

Answer 2

Try sorting both of the arrays using Title of the Movie (MergeSort), then merge both of them and modify the merge function so that it prints unique uncommon elements.

Answer 3

You might get better results using NSSet rather than NSArray, depending on whether or not you want to allow duplicates in your lists.

NSSet gives you methods like intersectsSet: which should give you what you need.

If you need union functionality, you can use NSMutableSet.