Check for missing number in sequence

Question

I have an List 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 missin

Answer 1

        List selectedNumbers = new List(){8, 5, 3, 12, 2};

        int firstNumber = selectedNumbers.OrderBy(i => i).First();
        int lastNumber = selectedNumbers.OrderBy(i => i).Last();

        List allNumbers = Enumerable.Range(firstNumber, lastNumber - firstNumber + 1).ToList();

        List missingNumbers = allNumbers.Except(selectedNumbers).ToList();

        foreach (int i in missingNumbers)
        {
            Response.Write(i);
        }