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.
A basic layout of the doubly linked list is shown in the below diagram.
Following are the 7 steps to add node at the end.
C++
|
/* Given a reference [pointer to pointer] to the head
of a DLL and an int, appends a new node at the end */
void append[Node** head_ref, int new_data]
{
/* 1. allocate node */
Node* new_node = new Node[];
Node* last = *head_ref; /* used in step 5*/
/* 2. put in the data */
new_node->data = new_data;
/* 3. This new node is going to be the last node, so
make next of it as NULL*/
new_node->next = NULL;
/* 4. If the Linked List is empty, then make the new
node as head */
if [*head_ref == NULL]
{
new_node->prev = NULL;
*head_ref = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last->next != NULL]
last = last->next;
/* 6. Change the next of last node */
last->next = new_node;
/* 7. Make last node as previous of new node */
new_node->prev = last;
return;
}
// This code is contributed by shivanisinghss2110
|
C
|
/* Given a reference [pointer to pointer] to the head
of a DLL and an int, appends a new node at the end */
void append[struct Node** head_ref, int new_data]
{
/* 1. allocate node */
struct Node* new_node = [struct Node*]malloc[sizeof[struct Node]];
struct Node* last = *head_ref; /* used in step 5*/
/* 2. put in the data */
new_node->data = new_data;
/* 3. This new node is going to be the last node, so
make next of it as NULL*/
new_node->next = NULL;
/* 4. If the Linked List is empty, then make the new
node as head */
if [*head_ref == NULL] {
new_node->prev = NULL;
*head_ref = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last->next != NULL]
last = last->next;
/* 6. Change the next of last node */
last->next = new_node;
/* 7. Make last node as previous of new node */
new_node->prev = last;
return;
}
|
Java
|
// Add a node at the end of the list
void append[int new_data]
{
/* 1. allocate node
* 2. put in the data */
Node new_node = new Node[new_data];
Node last = head; /* used in step 5*/
/* 3. This new node is going to be the last node, so
* make next of it as NULL*/
new_node.next = null;
/* 4. If the Linked List is empty, then make the new
* node as head */
if [head == null] {
new_node.prev = null;
head = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last.next != null]
last = last.next;
/* 6. Change the next of last node */
last.next = new_node;
/* 7. Make last node as previous of new node */
new_node.prev = last;
}
|
Python3
|
# Add a node at the end of the DLL
def append[self, new_data]:
# 1. allocate node 2. put in the data
new_node = Node[data = new_data]
last = self.head
# 3. This new node is going to be the
# last node, so make next of it as NULL
new_node.next = None
# 4. If the Linked List is empty, then
# make the new node as head
if self.head is None:
new_node.prev = None
self.head = new_node
return
# 5. Else traverse till the last node
while [last.next is not None]:
last = last.next
# 6. Change the next of last node
last.next = new_node
# 7. Make last node as previous of new node */
new_node.prev = last
# This code is contributed by jatinreaper
|
C#
|
// Add a node at the end of the list
void append[int new_data]
{
/* 1. allocate node
* 2. put in the data */
Node new_node = new Node[new_data];
Node last = head; /* used in step 5*/
/* 3. This new node is going
to be the last node, so
* make next of it as NULL*/
new_node.next = null;
/* 4. If the Linked List is empty,
then make the new * node as head */
if [head == null]
{
new_node.prev = null;
head = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last.next != null]
last = last.next;
/* 6. Change the next of last node */
last.next = new_node;
/* 7. Make last node as previous of new node */
new_node.prev = last;
}
// This code is contributed by shivanisinghss2110
|
Javascript
|
// Add a node at the end of the list
function append[new_data]
{
/* 1. allocate node
* 2. put in the data */
var new_node = new Node[new_data];
var last = head; /* used in step 5*/
/* 3. This new node is going to be the last node, so
* make next of it as NULL*/
new_node.next = null;
/* 4. If the Linked List is empty, then make the new
* node as head */
if [head == null] {
new_node.prev = null;
head = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last.next != null]
last = last.next;
/* 6. Change the next of last node */
last.next = new_node;
/* 7. Make last node as previous of new node */
new_node.prev = last;
}
// This code is contributed by Rajput-Ji
|
Six of the above 7 steps are same as the 6 steps used for inserting after a given node in singly linked list. The one extra step is needed to change previous pointer of new node.
4] Add a node before a given node:
Steps
Let the pointer to this given node be next_node and the data of the new node to be added as new_data.
- Check if the next_node is NULL or not. If it’s NULL, return from the function because any new node can not be added before a NULL
- Allocate memory for the new node, let it be called new_node
- Set new_node->data = new_data
- Set the previous pointer of this new_node as the previous node of the next_node, new_node->prev = next_node->prev
- Set the previous pointer of the next_node as the new_node, next_node->prev = new_node
- Set the next pointer of this new_node as the next_node, new_node->next = next_node;
- If the previous node of the new_node is not NULL, then set the next pointer of this previous node as new_node, new_node->prev->next = new_node
- Else, if the prev of new_node is NULL, it will be the new head node. So, make [*head_ref] = new_node.
Below is the implementation of the above approach:
Code block
Output:
Created DLL is:
Traversal in forward Direction
9 1 5 7 6
Traversal in reverse direction
6 7 5 1 9
A complete working program to test above functions.
Following is complete program to test above functions.
C++
|
// A complete working C++ program to
// demonstrate all insertion methods
#include
using namespace std;
// A linked list node
class Node
{
public:
int data;
Node* next;
Node* prev;
};
/* Given a reference [pointer to pointer]
to the head of a list
and an int, inserts a new node on the
front of the list. */
void push[Node** head_ref, int new_data]
{
/* 1. allocate node */
Node* new_node = new Node[];
/* 2. put in the data */
new_node->data = new_data;
/* 3. Make next of new node as head
and previous as NULL */
new_node->next = [*head_ref];
new_node->prev = NULL;
/* 4. change prev of head node to new node */
if [[*head_ref] != NULL]
[*head_ref]->prev = new_node;
/* 5. move the head to point to the new node */
[*head_ref] = new_node;
}
/* Given a node as prev_node, insert
a new node after the given node */
void insertAfter[Node* prev_node, int new_data]
{
/*1. check if the given prev_node is NULL */
if [prev_node == NULL]
{
coutnext = prev_node->next;
/* 5. Make the next of prev_node as new_node */
prev_node->next = new_node;
/* 6. Make prev_node as previous of new_node */
new_node->prev = prev_node;
/* 7. Change previous of new_node's next node */
if [new_node->next != NULL]
new_node->next->prev = new_node;
}
/* Given a reference [pointer to pointer] to the head
of a DLL and an int, appends a new node at the end */
void append[Node** head_ref, int new_data]
{
/* 1. allocate node */
Node* new_node = new Node[];
Node* last = *head_ref; /* used in step 5*/
/* 2. put in the data */
new_node->data = new_data;
/* 3. This new node is going to be the last node, so
make next of it as NULL*/
new_node->next = NULL;
/* 4. If the Linked List is empty, then make the new
node as head */
if [*head_ref == NULL]
{
new_node->prev = NULL;
*head_ref = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last->next != NULL]
last = last->next;
/* 6. Change the next of last node */
last->next = new_node;
/* 7. Make last node as previous of new node */
new_node->prev = last;
return;
}
// This function prints contents of
// linked list starting from the given node
void printList[Node* node]
{
Node* last;
cout8->6->4->NULL
insertAfter[head->next, 8];
cout data = new_data;
/* 3. Make next of new node as head and previous as NULL
*/
new_node->next = [*head_ref];
new_node->prev = NULL;
/* 4. change prev of head node to new node */
if [[*head_ref] != NULL]
[*head_ref]->prev = new_node;
/* 5. move the head to point to the new node */
[*head_ref] = new_node;
}
/* Given a node as prev_node, insert a new node after the
* given node */
void insertAfter[struct Node* prev_node, int new_data]
{
/*1. check if the given prev_node is NULL */
if [prev_node == NULL] {
printf["the given previous node cannot be NULL"];
return;
}
/* 2. allocate new node */
struct Node* new_node
= [struct Node*]malloc[sizeof[struct Node]];
/* 3. put in the data */
new_node->data = new_data;
/* 4. Make next of new node as next of prev_node */
new_node->next = prev_node->next;
/* 5. Make the next of prev_node as new_node */
prev_node->next = new_node;
/* 6. Make prev_node as previous of new_node */
new_node->prev = prev_node;
/* 7. Change previous of new_node's next node */
if [new_node->next != NULL]
new_node->next->prev = new_node;
}
/* Given a reference [pointer to pointer] to the head
of a DLL and an int, appends a new node at the end */
void append[struct Node** head_ref, int new_data]
{
/* 1. allocate node */
struct Node* new_node
= [struct Node*]malloc[sizeof[struct Node]];
struct Node* last = *head_ref; /* used in step 5*/
/* 2. put in the data */
new_node->data = new_data;
/* 3. This new node is going to be the last node, so
make next of it as NULL*/
new_node->next = NULL;
/* 4. If the Linked List is empty, then make the new
node as head */
if [*head_ref == NULL] {
new_node->prev = NULL;
*head_ref = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last->next != NULL]
last = last->next;
/* 6. Change the next of last node */
last->next = new_node;
/* 7. Make last node as previous of new node */
new_node->prev = last;
return;
}
// This function prints contents of linked list starting
// from the given node
void printList[struct Node* node]
{
struct Node* last;
printf["\nTraversal in forward direction \n"];
while [node != NULL] {
printf[" %d ", node->data];
last = node;
node = node->next;
}
printf["\nTraversal in reverse direction \n"];
while [last != NULL] {
printf[" %d ", last->data];
last = last->prev;
}
}
/* Driver program to test above functions*/
int main[]
{
/* Start with the empty list */
struct Node* head = NULL;
// Insert 6. So linked list becomes 6->NULL
append[&head, 6];
// Insert 7 at the beginning. So linked list becomes
// 7->6->NULL
push[&head, 7];
// Insert 1 at the beginning. So linked list becomes
// 1->7->6->NULL
push[&head, 1];
// Insert 4 at the end. So linked list becomes
// 1->7->6->4->NULL
append[&head, 4];
// Insert 8, after 7. So linked list becomes
// 1->7->8->6->4->NULL
insertAfter[head->next, 8];
printf["Created DLL is: "];
printList[head];
getchar[];
return 0;
}
|
Java
|
// A complete working Java program to demonstrate all
// Class for Doubly Linked List
public class DLL {
Node head; // head of list
/* Doubly Linked list Node*/
class Node {
int data;
Node prev;
Node next;
// Constructor to create a new node
// next and prev is by default initialized as null
Node[int d] { data = d; }
}
// Adding a node at the front of the list
public void push[int new_data]
{
/* 1. allocate node
* 2. put in the data */
Node new_Node = new Node[new_data];
/* 3. Make next of new node as head and previous as NULL */
new_Node.next = head;
new_Node.prev = null;
/* 4. change prev of head node to new node */
if [head != null]
head.prev = new_Node;
/* 5. move the head to point to the new node */
head = new_Node;
}
// Add a node before the given node
public void InsertBefore[Node next_node, int new_data]
{
/*Check if the given nx_node is NULL*/
if[next_node == null]
{
System.out.println["The given next node can not be NULL"];
return;
}
//Allocate node, put in the data
Node new_node = new Node[new_data];
//Making prev of new node as prev of next node
new_node.prev = next_node.prev;
//Making prev of next node as new node
next_node.prev = new_node;
//Making next of new node as next node
new_node.next = next_node;
//Check if new node is added as head
if[new_node.prev != null]
new_node.prev.next = new_node;
else
head = new_node;
}
/* Given a node as prev_node, insert
a new node after the given node */
public void InsertAfter[Node prev_Node, int new_data]
{
/*1. check if the given prev_node is NULL */
if [prev_Node == null] {
System.out.println["The given previous node cannot be NULL "];
return;
}
/* 2. allocate node
* 3. put in the data */
Node new_node = new Node[new_data];
/* 4. Make next of new node as next of prev_node */
new_node.next = prev_Node.next;
/* 5. Make the next of prev_node as new_node */
prev_Node.next = new_node;
/* 6. Make prev_node as previous of new_node */
new_node.prev = prev_Node;
/* 7. Change previous of new_node's next node */
if [new_node.next != null]
new_node.next.prev = new_node;
}
// Add a node at the end of the list
void append[int new_data]
{
/* 1. allocate node
* 2. put in the data */
Node new_node = new Node[new_data];
Node last = head; /* used in step 5*/
/* 3. This new node is going to be the last node, so
* make next of it as NULL*/
new_node.next = null;
/* 4. If the Linked List is empty, then make the new
* node as head */
if [head == null] {
new_node.prev = null;
head = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last.next != null]
last = last.next;
/* 6. Change the next of last node */
last.next = new_node;
/* 7. Make last node as previous of new node */
new_node.prev = last;
}
// This function prints contents of
// linked list starting from the given node
public void printlist[Node node]
{
Node last = null;
System.out.println["Traversal in forward Direction"];
while [node != null] {
System.out.print[node.data + " "];
last = node;
node = node.next;
}
System.out.println[];
System.out.println["Traversal in reverse direction"];
while [last != null] {
System.out.print[last.data + " "];
last = last.prev;
}
}
/* Driver program to test above functions*/
public static void main[String[] args]
{
/* Start with the empty list */
DLL dll = new DLL[];
// Insert 6. So linked list becomes 6->NULL
dll.append[6];
// Insert 7 at the beginning. So
// linked list becomes 7->6->NULL
dll.push[7];
// Insert 1 at the beginning. So
// linked list becomes 1->7->6->NULL
dll.push[1];
// Insert 4 at the end. So linked
// list becomes 1->7->6->4->NULL
dll.append[4];
// Insert 8, after 7. So linked
// list becomes 1->7->8->6->4->NULL
dll.InsertAfter[dll.head.next, 8];
// Insert 5, before 8.So linked
// list becomes 1->7->5->8->6->4
dll.InsertBefore[dll.head.next.next, 5];
System.out.println["Created DLL is: "];
dll.printlist[dll.head];
}
}
// This code is contributed by Sumit Ghosh
|
Python3
|
# A complete working Python
# program to demonstrate all
# insertion methods
# A linked list node
class Node:
# Constructor to create a new node
def __init__[self, data]:
self.data = data
self.next = None
self.prev = None
# Class to create a Doubly Linked List
class DoublyLinkedList:
# Constructor for empty Doubly Linked List
def __init__[self]:
self.head = None
# Given a reference to the head of a list and an
# integer, inserts a new node on the front of list
def push[self, new_data]:
# 1. Allocates node
# 2. Put the data in it
new_node = Node[new_data]
# 3. Make next of new node as head and
# previous as None [already None]
new_node.next = self.head
# 4. change prev of head node to new_node
if self.head is not None:
self.head.prev = new_node
# 5. move the head to point to the new node
self.head = new_node
# Given a node as prev_node, insert a new node after
# the given node
def insertAfter[self, prev_node, new_data]:
# 1. Check if the given prev_node is None
if prev_node is None:
print["the given previous node cannot be NULL"]
return
# 2. allocate new node
# 3. put in the data
new_node = Node[new_data]
# 4. Make net of new node as next of prev node
new_node.next = prev_node.next
# 5. Make prev_node as previous of new_node
prev_node.next = new_node
# 6. Make prev_node ass previous of new_node
new_node.prev = prev_node
# 7. Change previous of new_nodes's next node
if new_node.next:
new_node.next.prev = new_node
# Given a reference to the head of DLL and integer,
# appends a new node at the end
def append[self, new_data]:
# 1. Allocates node
# 2. Put in the data
new_node = Node[new_data]
# 3. This new node is going to be the last node,
# so make next of it as None
# [It already is initialized as None]
# 4. If the Linked List is empty, then make the
# new node as head
if self.head is None:
self.head = new_node
return
# 5. Else traverse till the last node
last = self.head
while last.next:
last = last.next
# 6. Change the next of last node
last.next = new_node
# 7. Make last node as previous of new node
new_node.prev = last
return
# This function prints contents of linked list
# starting from the given node
def printList[self, node]:
print["\nTraversal in forward direction"]
while node:
print[" {}".format[node.data]]
last = node
node = node.next
print["\nTraversal in reverse direction"]
while last:
print[" {}".format[last.data]]
last = last.prev
# Driver program to test above functions
# Start with empty list
llist = DoublyLinkedList[]
# Insert 6. So the list becomes 6->None
llist.append[6]
# Insert 7 at the beginning.
# So linked list becomes 7->6->None
llist.push[7]
# Insert 1 at the beginning.
# So linked list becomes 1->7->6->None
llist.push[1]
# Insert 4 at the end.
# So linked list becomes 1->7->6->4->None
llist.append[4]
# Insert 8, after 7.
# So linked list becomes 1->7->8->6->4->None
llist.insertAfter[llist.head.next, 8]
print ["Created DLL is: "]
llist.printList[llist.head]
# This code is contributed by Nikhil Kumar Singh[nickzuck_007]
|
C#
|
// A complete working C# program to demonstrate all
using System;
// Class for Doubly Linked List
public class DLL
{
Node head; // head of list
/* Doubly Linked list Node*/
public class Node
{
public int data;
public Node prev;
public Node next;
// Constructor to create a new node
// next and prev is by default initialized as null
public Node[int d]
{
data = d;
}
}
// Adding a node at the front of the list
public void push[int new_data]
{
/* 1. allocate node
* 2. put in the data */
Node new_Node = new Node[new_data];
/* 3. Make next of new node as
head and previous as NULL */
new_Node.next = head;
new_Node.prev = null;
/* 4. change prev of head node to new node */
if [head != null]
head.prev = new_Node;
/* 5. move the head to point to the new node */
head = new_Node;
}
/* Given a node as prev_node, insert
a new node after the given node */
public void InsertAfter[Node prev_Node, int new_data]
{
/*1. check if the given prev_node is NULL */
if [prev_Node == null]
{
Console.WriteLine["The given previous node cannot be NULL "];
return;
}
/* 2. allocate node
* 3. put in the data */
Node new_node = new Node[new_data];
/* 4. Make next of new node as next of prev_node */
new_node.next = prev_Node.next;
/* 5. Make the next of prev_node as new_node */
prev_Node.next = new_node;
/* 6. Make prev_node as previous of new_node */
new_node.prev = prev_Node;
/* 7. Change previous of new_node's next node */
if [new_node.next != null]
new_node.next.prev = new_node;
}
// Add a node at the end of the list
void append[int new_data]
{
/* 1. allocate node
* 2. put in the data */
Node new_node = new Node[new_data];
Node last = head; /* used in step 5*/
/* 3. This new node is going
to be the last node, so
* make next of it as NULL*/
new_node.next = null;
/* 4. If the Linked List is empty,
then make the new * node as head */
if [head == null]
{
new_node.prev = null;
head = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last.next != null]
last = last.next;
/* 6. Change the next of last node */
last.next = new_node;
/* 7. Make last node as previous of new node */
new_node.prev = last;
}
// This function prints contents of
// linked list starting from the given node
public void printlist[Node node]
{
Node last = null;
Console.WriteLine["Traversal in forward Direction"];
while [node != null] {
Console.Write[node.data + " "];
last = node;
node = node.next;
}
Console.WriteLine[];
Console.WriteLine["Traversal in reverse direction"];
while [last != null] {
Console.Write[last.data + " "];
last = last.prev;
}
}
/* Driver code*/
public static void Main[String[] args]
{
/* Start with the empty list */
DLL dll = new DLL[];
// Insert 6. So linked list becomes 6->NULL
dll.append[6];
// Insert 7 at the beginning.
// So linked list becomes 7->6->NULL
dll.push[7];
// Insert 1 at the beginning.
// So linked list becomes 1->7->6->NULL
dll.push[1];
// Insert 4 at the end. So linked list
// becomes 1->7->6->4->NULL
dll.append[4];
// Insert 8, after 7. So linked list
// becomes 1->7->8->6->4->NULL
dll.InsertAfter[dll.head.next, 8];
Console.WriteLine["Created DLL is: "];
dll.printlist[dll.head];
}
}
// This code is contributed by 29AjayKumar
|
Javascript
|
// A complete working javascript program to demonstrate all
// Class for Doubly Linked List
var head; // head of list
/* Doubly Linked list Node */
class Node {
// Constructor to create a new node
// next and prev is by default initialized as null
constructor[d] {
this.data = d;
this.next = null;
this.prev = null;
}
}
// Adding a node at the front of the list
function push[new_data] {
/*
* 1. allocate node 2. put in the data
*/
var new_Node = new Node[new_data];
/* 3. Make next of new node as head and previous as NULL */
new_Node.next = head;
new_Node.prev = null;
/* 4. change prev of head node to new node */
if [head != null]
head.prev = new_Node;
/* 5. move the head to point to the new node */
head = new_Node;
}
// Add a node before the given node
function InsertBefore[next_node , new_data] {
/* Check if the given nx_node is NULL */
if [next_node == null] {
document.write["The given next node can not be NULL"];
return;
}
// Allocate node, put in the data
var new_node = new Node[new_data];
// Making prev of new node as prev of next node
new_node.prev = next_node.prev;
// Making prev of next node as new node
next_node.prev = new_node;
// Making next of new node as next node
new_node.next = next_node;
// Check if new node is added as head
if [new_node.prev != null]
new_node.prev.next = new_node;
else
head = new_node;
}
/*
* Given a node as prev_node, insert a new node after the given node
*/
function InsertAfter[prev_Node , new_data] {
/* 1. check if the given prev_node is NULL */
if [prev_Node == null] {
document.write["The given previous node cannot be NULL "];
return;
}
/*
* 2. allocate node 3. put in the data
*/
var new_node = new Node[new_data];
/* 4. Make next of new node as next of prev_node */
new_node.next = prev_Node.next;
/* 5. Make the next of prev_node as new_node */
prev_Node.next = new_node;
/* 6. Make prev_node as previous of new_node */
new_node.prev = prev_Node;
/* 7. Change previous of new_node's next node */
if [new_node.next != null]
new_node.next.prev = new_node;
}
// Add a node at the end of the list
function append[new_data] {
/*
* 1. allocate node 2. put in the data
*/
var new_node = new Node[new_data];
var last = head; /* used in step 5 */
/*
* 3. This new node is going to be the last node, so make next of it as NULL
*/
new_node.next = null;
/*
* 4. If the Linked List is empty, then make the new node as head
*/
if [head == null] {
new_node.prev = null;
head = new_node;
return;
}
/* 5. Else traverse till the last node */
while [last.next != null]
last = last.next;
/* 6. Change the next of last node */
last.next = new_node;
/* 7. Make last node as previous of new node */
new_node.prev = last;
}
// This function prints contents of
// linked list starting from the given node
function printlist[node] {
var last = null;
document.write["
Traversal in forward Direction "];
while [node != null] {
document.write[node.data + " "];
last = node;
node = node.next;
}
document.write[];
document.write["
Traversal in reverse direction "];
while [last != null] {
document.write[last.data + " "];
last = last.prev;
}
}
/* Driver program to test above functions */
/* Start with the empty list */
// Insert 6. So linked list becomes 6->NULL
append[6];
// Insert 7 at the beginning. So
// linked list becomes 7->6->NULL
push[7];
// Insert 1 at the beginning. So
// linked list becomes 1->7->6->NULL
push[1];
// Insert 4 at the end. So linked
// list becomes 1->7->6->4->NULL
append[4];
// Insert 8, after 7. So linked
// list becomes 1->7->8->6->4->NULL
InsertAfter[head.next, 8];
// Insert 5, before 8.So linked
// list becomes 1->7->5->8->6->4
InsertBefore[head.next.next, 5];
document.write["Created DLL is:
"];
printlist[head];
// This code is contributed by Rajput-Ji
|
Output:
Created DLL is: Traversal in forward Direction 1 7 5 8 6 4 Traversal in reverse direction 4 6 8 5 7 1Also see: Delete a node in double Link List
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Article Tags :
Data Structures
Linked List
doubly linked list
Visa
Practice Tags :
Visa
Data Structures
Linked List