Question

Array 1 | Array 2 =================    1    |   2    2    |   3    3    |   4    5    |   5         |   6 

What is a good algorithm to ‘sync’ or combine Array 2 into Array 1? The following needs to happen:

1. Integers in Array 2 but not in Array 1 should be added to Array 1.
2. Integers in both Arrays can be left alone.
3. Integers in Array 1 but not in Array 2 should be removed from Array 1.

I’ll eventually be coding this in Obj-C, but I’m really just looking for a pseudo-code representation of an efficient algorithm to solve this problem so feel free to suggest an answer in whatever form you’d like.

EDIT:

The end result I need is bit hard to explain without giving the backstory. I have a Cocoa application that has a Core Data entity whose data needs to be updated with data from a web service. I cannot simply overwrite the contents of Array 1 (the core data entity) with the content of Array 2 (the data parsed from the web into an array) because the Array 1 has relationships with other core data entities in my application. So basically it is important that integers contained in both Arrays are not overwritten in array one.

Answer 1

I’m kind of guessing since your example leaves some things up in the air, but typically in situations like this I would use a set. Here’s some example code in Obj-C.

NSMutableSet *set = [NSMutableSet set]; [set addObjectsFromArray:array1]; [set addObjectsFromArray:array2]; NSArray *finalArray = [[set allObjects] sortedArrayUsingSelector:@selector(compare:)];