[].index(nil) returns nil. nil || 0 would give you 0. [].delete_at(0) is a no-op where as [].delete_at(nil) throws an exception.

You need to return an integer, not a string.

An articulated and helpful comment, even if it were criticism, is always welcome, thanks! :)

Thanks mate! Im a noob and didn't know that. Will keep it in mind!