# Explain the difference between a singly linked list and a doubly linked list.

In computer science, a linked list is an important data structure for organizing and storing data. The linked list is a series of nodes where each node contains a data element as well as a link to the next node. There are many types of linked lists, but the two most common ones are single-linked lists and double-linked lists. This comprehensive explanation will explore the differences between both types of linked list.  Data Structures and Algorithms With C++ Classes in Pune

The simpler type is a singly linked list. It is made up of nodes, where each node has two fields.

1. Data This field contains the data or value that is associated with the node.
2. Next This field contains a reference to the node following the current one. It is a pointer to the memory address where the next node will be stored.

The first node of a singly-linked list is known as the “head,” while the `Next` fields on the last node are usually null values, which indicate the end. Here are some of the key characteristics of singly-linked lists:

1. Traversal : To traverse an singly linked list you begin at the head node, and then follow the `Next` pointers to the end. This process has a linear time complexity of O(n), where the number of nodes is n.
2. Memory Efficiency : Single-linked lists require less memory than double-linked lists, because they only need one reference field for each node (the `Next` arrow).
3. Ease Of Insertion/Deletion : It is relatively easy to add and delete nodes in a list of singly linked nodes, especially if there is a reference for the node that comes before the node you wish to modify.
4. Unidirectional : The main disadvantage of singly-linked lists is that you can only traverse in one direction, which is forward. You’ll need another data structure if you want to navigate in both directions.

A doubly-linked list, however, adds an additional field of reference to each node, extending the functionality of a singlely-linked list. Each node in a doubly-linked list contains three fields. Data Structures and Algorithms With C++ Course in Pune

1. Data : This field contains the data or value that is associated with each node.
2. Next This field indicates the next node of the sequence. It works like a singly-linked list.
3. Previous This is a brand new field in a double linked list. It indicates the previous node of the sequence.

Double-linked lists have some unique characteristics.

1. Traversal Supports bidirectional traversal. Start at the top or bottom of the list, and then follow the `Next` and `Previous` pointers in either direction. They are more flexible for some applications, but at the expense of memory consumption and complexity.
2. Memory overhead Due to the additional `Prior` pointers in doubly linked list, they consume more memory. This is an issue if memory consumption is critical to your application.
3. Ease in Inserting/Deleting: Double-linked lists offer more flexibility for inserting or deleting nodes. In some cases, it is more efficient to perform these operations if you have access to the previous and next nodes.
4. Additional Operation: Double linked lists allow for additional operations not possible in singly-linked lists. These include reversing a list, deleting nodes by referencing them only (no need to traverse the list from the previous node), or implementing data structures such as doubly ended queues.

Use cases:

Your application will determine whether you choose a single-linked list or a doubly linked list. Here are some examples of common uses for each type.

Lists with only one link:

1. Memory Efficiency Use singly-linked lists when memory is an issue and you do not need bidirectional traversal.
2. Simple iteration : A singly linked list will work if you need to navigate the list only in one direction.
3. Queues and Stacks Singly-linked lists are commonly used as the data structure underlying stacks and queuing.  Data Structures and Algorithms With C++ Training in Pune