Question

I’ve read a couple of articles stating that List.RemoveAt() is in O(n) time.

If I do something like:

var myList = new List<int>();

/* Add many ints to the list here. */

// Remove item at end of list:
myList.RemoveAt(myList.Count - 1); // Does this line run in O(n) time?

Removing from the end of the list should be O(1), as it just needs to decrement the list count.

Do I need to write my own class to have this behavior, or does removing the item at the end of a C# list already perform in O(1) time?

Answer 1

In general List<T>::RemoveAt is O(N) because of the need to shift elements after the index up a slot in the array. But for the specific case of removing from the end of the list no shifting is needed and it is consequently O(1)