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

for a List L a general solution (works in all programming languages) would be simply

L.Count()*(L.Count()+1)/2 - L.Sum();

which returns the expected sum of series minus the actual series.

for a List of size n the missing number is:

n(n+1)/2 - (sum of list numbers)