Is it necessary to have a tail pointer in doubly linked list? How to implement doubly linked list insertion without tail pointer, what would be the time complexity if we do so.
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2 Answers
If you know the node you're inserting before or after, then complexity is O(1). You only set the pointers in the previous/next nodes to point to the new node, and set the pointers in the new node to the prev/next nodes. You also update the head pointer if insertion is to the beginning of the list.
If you do not have a tail pointer in a doubly-linked list (or singly-linked list) and you do not have a reference to the last element, then appending to the list becomes O(n) because you have to traverse the list to find the last element.
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No, it is not necessary. Below are the time complexities for a doubly-linked list that does not utilize tail pointers.
Prepending to a List: O(1)
(head <-> newNode <-> x)
Inserting between two nodes in the List: O(n)
(head <-> x <-> newNode <-> y)
Appending to a List: O(n)
(head <-> x <-> y <-> newNode)
Note: Utilizing the
tailof a doubly-linked list would make the complexity O(1)
TL;DR: No, it would function almost the same, except for less performant appending cases O(n).
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