What is the difference between a singly and a doubly linked list?

A singly linked list allows traversal in one direction only, while a doubly linked list allows traversal in both directions.

A singly linked list is a type of data structure in which each node contains a data element and a reference (link) to the next node in the sequence. This allows for efficient insertion and removal of elements from any position in the sequence during iteration. However, it only allows for one-way traversal, meaning you can only navigate the list in the direction from the first node (head) to the last node (tail). If you need to traverse the list in the opposite direction, you would have to start from the head again and move through the list until you reach your desired node.

On the other hand, a doubly linked list is a more complex type of linked list which contains a link to the next as well as the previous node in the sequence. This means you can traverse the list in both directions, from the head to the tail and vice versa. This two-way traversal makes it easier to navigate the list and perform operations like insertion and deletion at both ends of the list, but it also requires more memory to store the additional previous node reference.

In terms of memory usage, a singly linked list is more memory-efficient as it only needs to store a single reference to the next node. A doubly linked list, however, needs to store two references for each node: one for the next node and one for the previous node. This makes doubly linked lists less memory-efficient.

In terms of use cases, singly linked lists are often used in scenarios where memory is a concern and where one-way traversal is sufficient, such as implementing a stack. Doubly linked lists, on the other hand, are used in scenarios where two-way traversal is needed, such as implementing a browser's back and forward navigation buttons.

In summary, the choice between a singly and doubly linked list depends on the specific requirements of your application, including memory constraints and the need for one-way or two-way traversal.