Traversing a doubly linked list is generally faster than traversing a singly linked list, but the speedup depends on how you do the traversal:
- Traversing from first to last node: No difference.
- Random access: Doubly linked list is faster, the difference is a fixed factor. (Like twice as fast. Which makes it still very slow for random access compared to arrays.)
- Reverse order: Doubly linked list is just as fast traversing "backwards" as "forwards", while a singly linked list traversing in reverse order needs to traverse the entire list once for every element in the list - it is a LOT slower. (Time complexity O(n) for doubly linked list, O(n*n) for singly linked, if you are familiar with the notation.)
If you are talking about the computer science "big O notation", doubly linked and singly liked lists are the same. This is because the Big O notation ignores fixed factors and only looks at how time increases with the length of the list, and in this respect the two are the same. (Except for the special case of traversing the list in reverse order. Even here a singly linked list could do it in O(n) time - same as a doubly linked list - by reversing the list (O(n)) before traversing it (O(n)) for a total time of 2*O(n), which by the rules of Big O is the same as O(n).)
