C#: how do you check lists are the same size & same elements?

Question

There are two lists of string

List<string> A;
List<string> B;

What is the shortest code you would suggest to check that A.Count == B.Count and each element of A in B and vise versa: every B is in A (A items and B items may have different order).

Answer 1

If you don't need to worry about duplicates:

bool equal = new HashSet<string>(A).SetEquals(B);

If you are concerned about duplicates, that becomes slightly more awkward. This will work, but it's relatively slow:

bool equal = A.OrderBy(x => x).SequenceEquals(B.OrderBy(x => x));

Of course you can make both options more efficient by checking the count first, which is a simple expression. For example:

bool equal = (A.Count == B.Count) && new HashSet<string>(A).SetEquals(B);

... but you asked for the shortest code :)

Answer 2

A.Count == B.Count && new HashSet<string>(A).SetEquals(B);

If different frequencies of duplicates are an issue, check out this question.