The function returns false for your example, as stated i testcase number 8. This is correct in my oppinion but for the tests to pass it is.

I think this will fail with numbers that start with a zero: 01.02.03.04

Lol my point is that someone changed the C# test case and broke ur solution along with many other solutions. Cause none of the solutions i checked works now(not just yours)

That may be so, but at least it doesn't use string operations which can't be best practice for a "number" problem. But I agree that if the scanrio is large numbers a differnt solution has to be used.

doesnt work... takes 2 long

This seems to generate a StackOverflow in VS for more than 5 digits.

Very nice.