Question

I have a private LinkedList in a Java class & will frequently need to retrieve the last element in the list. The lists need to scale, so I’m trying to decide whether I need to keep a reference to the last element when I make changes (to achieve O(1)) or if the LinkedList class does that already with the getLast() call.

What is the big-O cost of LinkedList.getLast() and is it documented? (i.e. can I rely on this answer or should I make no assumptions & cache it even if it’s O(1)?)

Answer 1

It is O(1) because the list is doubly-linked. It keeps references to both head and tail.

From documentation:

Operations that index into the list will traverse the list from the beginning or the end, whichever is closer to the specified index.