Answer:
O(n)
Explanation:
If we wish to calculate the size of a list data structure where no count is available then the size operation will have a time complexity of O(n) where 'n' represents the number of existing elements of the list. This is because the operation will involve iterating through the entire list of size n via pointers till we reach the end of the list. So the time complexity will be n*O(1) or O(n).
