Singly vs Doubly Linked Lists
A linear collection of data elements whose order is not given by their physical placement in memory.
Linked lists connect nodes through pointers
A linked list stores each value inside a node, and each node points to the next one. Unlike arrays, the nodes do not need to sit next to each other in memory. Traversal works by following links from one node to the next, which makes the pointer structure more important than physical placement.
In Singly mode, each node only shows a next link, so the arrows move forward.
In Doubly mode, each node also stores a prev link, so the diagram can show movement in both directions.
The active node is highlighted so you can see exactly where traversal or deletion is happening.
In the traversal tab, press Move Backward in singly mode and notice that the explanation tells you why the move is impossible.
Switch to doubly mode and try the same action again to see how the extra previous pointer changes the result.
In the deletion and tradeoff tabs, compare how many pointer updates and how much extra memory each structure needs.
Explore traversal, deletion, and pointer-cost tradeoffs without changing the underlying teaching flow.
Question It Answers
“Why can’t I go backwards in a singly linked list?”
One extra pointer changes how the list behaves
Both structures store data as linked nodes, but the extra previous pointer in a doubly linked list changes traversal, deletion, and memory usage. That is the main tradeoff the interactive module is trying to make visible.
Stores less pointer metadata in each node.
Traversal naturally moves forward one node at a time.
Operations that need the previous node become less convenient.
Supports traversal in both directions.
Deleting or rewiring a known node is easier because both neighbors are linked.
The tradeoff is extra memory and more pointers to maintain on updates.
| Aspect | Singly Linked List | Doubly Linked List |
|---|---|---|
| Pointers stored | One next pointer per node. | One next pointer and one previous pointer per node. |
| Traversal direction | Forward only. | Forward and backward. |
| Delete a known node | Usually needs access to the previous node to rewire links. | Can update both sides directly once the node is known. |
| Memory cost | Lower overhead because each node stores fewer references. | Higher overhead because each node stores an extra pointer. |
| Best fit | Simple forward traversal with minimal memory. | Bidirectional traversal and easier local updates. |
The short version
- A linked list connects nodes with pointers instead of storing them in one contiguous block.
- A singly linked list can move forward, but it cannot move backward because no previous link is stored.
- A doubly linked list uses more memory per node, but the extra previous pointer makes reverse traversal possible.
- Deletion is a good tradeoff example: singly lists are lighter, while doubly lists make local rewiring easier.