Question

I have an List<int> which contains 1,2,4,7,9 for example.

I have a range from 0 to 10.

Is there a way to determine what numbers are missing in that sequence?

I thought LINQ might provide an option but I can’t see one

In the real world my List could contain 100,000 items so performance is key

Answer 1

var list = new List<int>(new[] { 1, 2, 4, 7, 9 });
var result = Enumerable.Range(0, 10).Except(list);