What is the most efficient way to compare/sort items from two arrays?

Question

I have a question about efficient implementation. Lets say I have two arrays:

One array is all possible items in a house: Table, Chair, TV, Fireplace, Bed

The other is an array of items in a particular house: Table, TV, Bed

I also have two list boxes:

1. listbox for items in the house - the "HAS" list box
2. listbox items not in the house - the "NEEDS" list box

I need to list the items already in the house in the "HAS" list box as well as the items that are NOT in the house in the "NEEDS" list box. It seems to me that nested "For each" loops would be a start to solving this problem but I am not exactly sure which case needs to be nested. What is the most efficient way to accomplish a task like this?

Answer 1

var allList = (new [] {"Table", "Chair", "TV", "Fireplace", "Bed"}).ToList();
var hasList = (new [] {"Table", "Chair"}).ToList();

var hasSet = new HashSet<string>(hasList);
var needsList = allList.Where(i => !hasList.Contains(i)).ToList();

That's ~ the fastest solution (at least, in big O notation).

Answer 2

var allItems = (new [] {"Table", "Chair", "TV", "Fireplace", "Bed"});
var hasItems = (new [] {"Table", "Chair"});

var hasList = hasItems.ToList();
var needsList = allItems.Except(hasItems).ToList();