Doubly Linked In C++ As in the singly linked list, the doubly linked list also has a head and a tail. The previous pointer of the head is set to NULL as this is the first node. The next pointer of the tail node is set to NULL as this is the last node.
How do you find the tail node in a doubly linked list?
addNode[] will add node to the list:
- It first checks whether the head is null, then it will insert the node as the head.
- Both head and tail will point to a newly added node.
- Head’s previous pointer will point to null and tail’s next pointer will point to null.
What is the disadvantage of doubly linked list?
Disadvantages Of DLL: It uses extra memory when compared to the array and singly linked list. Since elements in memory are stored randomly, therefore the elements are accessed sequentially no direct access is allowed.
How do you find the tail of a linked list?
The first and last node of a linked list usually are called the head and tail of the list, respectively. Thus, we can traverse the list starting at the head and ending at the tail. The tail node is a special node, where the next pointer is always pointing or linking to a null reference, indicating the end of the list.
Do doubly linked lists need a tail?
A Doubly linked list is a linked list that consists of a set of sequentially linked records called nodes. Each node contains two fields that are references to the previous and to the next node in the sequence of nodes. Also, we need to maintain two pointers, head [points to first node] and tail [points to last node].
What is the tail of a doubly linked list?
Just like the Singly Linked List, the first node in the Doubly Linked List is also called the head and the last node is also called the tail. In Doubly Linked List each node stores three things, data [integer or string], a reference to the next node and a previous node.
What is the advantage of double linked list?
Following are advantages/disadvantages of doubly linked list over singly linked list. 1] A DLL can be traversed in both forward and backward direction. 2] The delete operation in DLL is more efficient if pointer to the node to be deleted is given. 3] We can quickly insert a new node before a given node.
What is tail in doubly linked list?
How do you insert a node at the tail of a linked list?
Algorithm
- Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
- Create another class InsertEnd which has two attributes: head and tail.
- addAtEnd[] will add a new node at the end of the list: Create a new node.
- display[] will display the nodes present in the list:
What is the advantage of having a tail reference in a linked list?
tail. next would be a synonym for head , so it’s not really saving space, nor is it really costing much space. One possible advantage is that it is a little easier to understand how the push and pop operations work with a doubly-linked list.
Which operation is more efficient in doubly linked list?
While adding or removing a node in a doubly linked list requires changing more links than the same operations on a singly linked list, the operations are simpler and potentially more efficient [for nodes other than first nodes] because there is no need to keep track of the previous node during traversal or no need to …
Which is an example of a doubly linked list?
Since each node has pointers in both the direction, doubly linked list can be traversed in both forward and backward directions. Figure 1 shows an example of a doubly linked list containing 2 items. Fig 1: An example of a doubly linked list The first node is pointed by a pointer called head and the last node is pointed by a pointer called tail.
How to insert a node in a doubly linked list?
Linked List Introduction. Inserting a node in Singly Linked List. A Doubly Linked List [DLL] contains an extra pointer, typically called previous pointer, together with next pointer and data which are there in singly linked list. Following is representation of a DLL node in C language.
What’s the difference between DLL and singly linked list?
A D oubly L inked L ist [DLL] contains an extra pointer, typically called previous pointer, together with next pointer and data which are there in singly linked list. Following is representation of a DLL node in C language. Following are advantages/disadvantages of doubly linked list over singly linked list.
How to delete a node in a singly linked list?
In singly linked list, to delete a node, pointer to the previous node is needed. To get this previous node, sometimes the list is traversed. In DLL, we can get the previous node using previous pointer. 1] Every node of DLL Require extra space for an previous pointer. It is possible to implement DLL with single pointer though [See this and this ].
Insertion in doubly linked lists is similar to what we saw in the singly linked list with two exceptions:
- We must update both the previous and next pointers in all affected nodes.
- We can use the tail pointer to make the insertion of data at the end of the list very efficient.
Inserting at the Beginning
Inserting at the beginning of a doubly linked list is almost as straightforward as in a singly linked list. We just need to make sure that we update the previous pointer in each affected node. After creating the new node in line 1, we check to see if the list is empty in line 2. If it is empty, then we only have to worry about updating the head and tail pointers to both point at node in lines 3 and 4. If the list is not empty, we have the situation shown below.
To insert a node at the beginning of the list, we set head.previous [the previous pointer in the first node in the list] to point to the new node in line 5.
Next, we set the next pointer in the new node to point to where head is currently pointing in line 6, which is the first node in the list.
Finally, we update head to point to the new node and then increment the size in line 8.
With a little bit of reformatting, we can see that we’ve successfully inserted our new node in the list.
The pseudocode for this operation is given below.
function prepend[data] node = new Node[data] [1] if size == 0 [2] head = node [3] tail = node [4] else head.previous = node [5] node.next = head [6] head = node [7] end size = size + 1 [8] end function
Since there are no loops in the prepend code, the code runs in constant time.
Inserting in the Middle
Inserting a new node at some arbitrary index in a doubly linked list is similar to the same operation in a singly linked list with a couple of changes.
- If the index is at the end of the list, we can use an efficient append operation [defined below] to insert the node at the end of the list.
- When walking through the list to the correct index, we do not need to keep track of the previous node.
- We will have to update both the previous and next pointers in all affected nodes.
Lines 1 and 2 in the code check to ensure that the index is a valid number, then we check to see if we are inserting at the beginning or end of the list in lines 2 and 4. If we are, we simply call the appropriate method, either prepend or append.
If none of those conditions exist, then we start the process of walking through the list to find the node at index. To do this, we need to create the new node we want to insert and then create a temporary pointer curr that we will use to point to the current node on our walk.
Lines 10 and 11 form the loop that walks through the list until we get to the desired index. When the loop ends, we will want to insert the new node between curr and curr.next. Thus, we set the appropriate values for the new node’s next and previous pointers in line 12 and 13. Then, we set the previous pointer in node.next to point back to node in line 14 and then set curr.next to point at the new node. Finally, we increment size by 1.
function insertAt[data, index] if index < 0 OR index > size [1] raise exception [2] else if index == 0 [3] prepend[data] [4] else if index == size [5] append[data] [6] else [7] node = new node[data] [8] curr = head [9] for i = 1 to index -1 [10] curr = curr.next [11] end for node.next = curr.next [12] node.previous = curr [13] node.next.previous = node [14] curr.next = node [15] size = size + 1 [16] end if end function
Although prepend and append run in constant time, the general case will cause us to walk through the list using a for loop. Therefore, the insertAt operation runs in order $N$ time.
Inserting at the End
Since we have added the tail pointer to the doubly linked list class, we can make adding a node at the end of the list run in constant time instead of order $N$ time. In fact, if you look at the code below for the append operation, it is exactly the same as the constant time prepend operation except we have replaced the head pointer with the tail pointer in lines 5 – 7.
function append[data] node = new node[data] [1] if size == 0 [2] tail = node [3] head = node [4] else tail.next = node [5] node.previous = tail [6] tail = node [7] end if size = size + 1 [8] end function