What are circular doubly linked lists?

Answer 1

circular linked list is type of linked list used in data structure where address of 1st node is stored in the link part of last node

data1link1 ................... datanlinkn

address1 here linkn=adress1

(node1) (noden)

pratima patwa

Answer 2

A circular linked list allows constant-time access to both the head and tail of a list through a single pointer to the tail. Being circular, the tail node points "forwards" to the head node. In a doubly-linked list, the head also points "backwards" to the tail.

Answer 3

A circular linked list is just a linked list in which the last element of the list is connected to the first element, so if you followed the links, you'd be following them in a circle forever.

Answer 4

Doubly linked lists are composed from nodes. Each node refers to a data element of type T, and has two node pointers, conventionally named next and prev:

template<typename T>

struct node {

T data;

node* next;

node* prev;

};

With a normal doubly linked list, the head node's prev pointer and the tail node's next pointer are both assigned the null address because nothing can come before the head node or after the tail node. When inserting at the head of the list, the new node's next node points to the current head node, while the current head node's prev node points to the new node. The new node then becomes the new head of the list. Similarly when inserting at the tail, the new node's prev node points to the old tail, the old tail's next node points to the new node and the new node becomes the tail. Both operations are constant time operations. Inserting anywhere else requires linear traversal to the insertion point, and the new node can be inserted either before or after that node. Given that nothing comes after the tail, traversing forwards from any node means that we must stop traversing when we reach the tail. Similarly when traversing backwards, we stop traversing when we reach the head. In order to allow constant time insertion at the head or tail, we must keep track of the head and tail nodes.

With a circular doubly linked list, the head node's prev pointer refers to the tail node while the tail node's next pointer refers to the head node. In this way, we can traverse forwards or backwards from any node in an endless loop; we simply need to keep track of the node we start traversing from to know when we've performed a complete traversal. Moreover, we no longer need to keep track of both the head and tail because the head node always refers to the tail node (and vice versa). Typically we only keep track of the head node. Insertions can also be done before or after any existing node including the head and tail. The only complication is when inserting after the tail or before the head (which is effectively the same position in a circular list), we need to decide whether the new node should become the new head or the new tail. Typically, if it comes after the tail, then it becomes the new tail, otherwise it becomes the new head.

A classic example of the application of circular doubly linked lists can be found in Donald Knuth's Dancing Links algorithm, which uses nodes that point up, down, left and right to form a sparse matrix of 0s and 1s (the data) with endless traversal in any direction (both vertically and horizontally). Essentially, every row and column is itself a circular doubly linked list and the entire structure can be imagined as being a Toroid (a ring doughnut shape). Nodes that represent 1s are the only nodes of any interest to the algorithm and these are the nodes that are actually linked to one another. Nodes representing 0 play no part in the algorithm and since we cannot traverse to them we do not need to create them (we can imagine them as being placeholders between the nodes with 1s). This structure allows rapid traversal between the 1s across any row or column, forwards or backwards; we simply need to know which row and column the node is in to identify its meaning with respect to the algorithm.

Answer 5

Circular linked lists provide constant time access to the both the head and the tail of the list using a single point of reference (the tail). With singly linked lists, you only have constant time access to the head unless you use a second point of reference to the tail. That uses more memory than a circular linked list because the tail always points to the head, so you get constant time access to both.

Answer 6

A Circular linked list is a type of linked list used in the data structure where the address of the first node is stored in the linked part of the last node.