Hash function on list independant of order of items in it

Question

I want to have a dictionary that assigns a value to a set of integers.

For example key is [1 2 3] and value will have certain

Answer 1

Use a HashSet<T> and HashSet<T>.CreateSetComparer(), which returns an IEqualityComparer<HashSet<T>>.

Answer 2

Create your own type that implements IEnumerable<T>.

Override GetHashCode. In it, sort your collection, call and return ToArray().GetHashCode().

Answer 3

If the range of the values in key happens to be limited to low-ish positive integers, you could map each one to a prime number using a simple lookup, then multiply them together to arrive at the value.

Using the example in the question:

[1, 2, 3] maps to 2 x 3 x 5 = 30
[3, 2, 1] maps to 5 x 3 x 2 = 30