Find "not the same" elements in two arrays

Question

I have two integer lists (List<int>). They contain the same elements, but List 1 contains elements that are not in the List 2.

How to find which elements of the List 1 ARE NOT in the List 2.

Thanks :)

PS. lang is c#

Answer 1

You can use IEnumerable.Except:

list1.Except(list2);

Answer 2

new HashSet<int>(l1).ExceptWith(l2);