# Reverse a Doubly Linked List

Write a C function to reverse a given Doubly Linked List

See below diagrams for example.

`     (a) Original Doubly Linked List  ` `     (b) Reversed Doubly Linked List  ` Here is a simple method for reversing a Doubly Linked List. All we need to do is swap prev and next pointers for all nodes, change prev of the head (or start) and change the head pointer in the end.

## C++

 `/* C++ program to reverse a doubly linked list */` `#include ` `using` `namespace` `std; ` ` `  `/* a node of the doubly linked list */` `class` `Node  ` `{  ` `    ``public``: ` `    ``int` `data;  ` `    ``Node *next;  ` `    ``Node *prev;  ` `};  ` ` `  `/* Function to reverse a Doubly Linked List */` `void` `reverse(Node **head_ref)  ` `{  ` `    ``Node *temp = NULL;  ` `    ``Node *current = *head_ref;  ` `     `  `    ``/* swap next and prev for all nodes of  ` `    ``doubly linked list */` `    ``while` `(current != NULL)  ` `    ``{  ` `        ``temp = current->prev;  ` `        ``current->prev = current->next;  ` `        ``current->next = temp;              ` `        ``current = current->prev;  ` `    ``}  ` `     `  `    ``/* Before changing head, check for the cases like empty  ` `        ``list and list with only one node */` `    ``if``(temp != NULL )  ` `        ``*head_ref = temp->prev;  ` `}  ` ` `  ` `  ` `  `/* UTILITY FUNCTIONS */` `/* Function to insert a node at the ` `beginging of the Doubly Linked List */` `void` `push(Node** head_ref, ``int` `new_data)  ` `{  ` `    ``/* allocate node */` `    ``Node* new_node = ``new` `Node(); ` ` `  `    ``/* put in the data */` `    ``new_node->data = new_data;  ` `     `  `    ``/* since we are adding at the begining,  ` `    ``prev is always NULL */` `    ``new_node->prev = NULL;  ` ` `  `    ``/* link the old list off the new node */` `    ``new_node->next = (*head_ref);      ` ` `  `    ``/* change prev of head node to new node */` `    ``if``((*head_ref) != NULL)  ` `    ``(*head_ref)->prev = new_node ;  ` ` `  `    ``/* move the head to point to the new node */` `    ``(*head_ref) = new_node;  ` `}  ` ` `  `/* Function to print nodes in a given doubly linked list  ` `This function is same as printList() of singly linked lsit */` `void` `printList(Node *node)  ` `{  ` `    ``while``(node != NULL)  ` `    ``{  ` `        ``cout << node->data << ``" "``;  ` `        ``node = node->next;  ` `    ``}  ` `}  ` ` `  `/* Driver code */` `int` `main()  ` `{  ` `    ``/* Start with the empty list */` `    ``Node* head = NULL;  ` `     `  `    ``/* Let us create a sorted linked list to test the functions  ` `    ``Created linked list will be 10->8->4->2 */` `    ``push(&head, 2);  ` `    ``push(&head, 4);  ` `    ``push(&head, 8);  ` `    ``push(&head, 10);  ` `     `  `    ``cout << ``"Original Linked list"` `<< endl;  ` `    ``printList(head);  ` `     `  `    ``/* Reverse doubly linked list */` `    ``reverse(&head);  ` `     `  `    ``cout << ````" Reversed Linked list"``` `<< endl;  ` `    ``printList(head);          ` `     `  `    ``return` `0; ` `}  ` ` `  `// This code is contributed by rathbhupendra `

## C

 `/* Program to reverse a doubly linked list */` `#include ` `#include ` ` `  `/* a node of the doubly linked list */` `struct` `Node ` `{ ` `  ``int` `data; ` `  ``struct` `Node *next; ` `  ``struct` `Node *prev;     ` `}; ` ` `  `/* Function to reverse a Doubly Linked List */` `void` `reverse(``struct` `Node **head_ref) ` `{ ` `     ``struct` `Node *temp = NULL;   ` `     ``struct` `Node *current = *head_ref; ` `      `  `     ``/* swap next and prev for all nodes of  ` `       ``doubly linked list */` `     ``while` `(current !=  NULL) ` `     ``{ ` `       ``temp = current->prev; ` `       ``current->prev = current->next; ` `       ``current->next = temp;               ` `       ``current = current->prev; ` `     ``}       ` `      `  `     ``/* Before changing head, check for the cases like empty  ` `        ``list and list with only one node */` `     ``if``(temp != NULL ) ` `        ``*head_ref = temp->prev; ` `}      ` ` `  ` `  ` `  `/* UTILITY FUNCTIONS */` `/* Function to insert a node at the beginging of the Doubly Linked List */` `void` `push(``struct` `Node** head_ref, ``int` `new_data) ` `{ ` `    ``/* allocate node */` `    ``struct` `Node* new_node = ` `            ``(``struct` `Node*) ``malloc``(``sizeof``(``struct` `Node)); ` `  `  `    ``/* put in the data  */` `    ``new_node->data  = new_data; ` `     `  `    ``/* since we are adding at the begining,  ` `      ``prev is always NULL */` `    ``new_node->prev = NULL; ` `  `  `    ``/* link the old list off the new node */` `    ``new_node->next = (*head_ref);     ` ` `  `    ``/* change prev of head node to new node */` `    ``if``((*head_ref) !=  NULL) ` `      ``(*head_ref)->prev = new_node ;     ` `  `  `    ``/* move the head to point to the new node */` `    ``(*head_ref)    = new_node; ` `} ` ` `  `/* Function to print nodes in a given doubly linked list  ` `   ``This function is same as printList() of singly linked lsit */` `void` `printList(``struct` `Node *node) ` `{ ` `  ``while``(node!=NULL) ` `  ``{ ` `   ``printf``(``"%d "``, node->data); ` `   ``node = node->next; ` `  ``} ` `}  ` ` `  `/* Drier program to test above functions*/` `int` `main() ` `{ ` `  ``/* Start with the empty list */` `  ``struct` `Node* head = NULL; ` `  `  `  ``/* Let us create a sorted linked list to test the functions ` `   ``Created linked list will be 10->8->4->2 */` `  ``push(&head, 2); ` `  ``push(&head, 4); ` `  ``push(&head, 8); ` `  ``push(&head, 10); ` `  `  `  ``printf``(````" Original Linked list "````); ` `  ``printList(head); ` `  `  `  ``/* Reverse doubly linked list */` `  ``reverse(&head); ` `  `  `  ``printf``(````" Reversed Linked list "````); ` `  ``printList(head);            ` `  `  `  ``getchar``(); ` `} `

## Java

 `// Java program to reverse a doubly linked list ` ` `  `class` `LinkedList { ` ` `  `    ``static` `Node head; ` ` `  `    ``static` `class` `Node { ` ` `  `        ``int` `data; ` `        ``Node next, prev; ` ` `  `        ``Node(``int` `d) { ` `            ``data = d; ` `            ``next = prev = ``null``; ` `        ``} ` `    ``} ` ` `  `    ``/* Function to reverse a Doubly Linked List */` `    ``void` `reverse() { ` `        ``Node temp = ``null``; ` `        ``Node current = head; ` ` `  `        ``/* swap next and prev for all nodes of  ` `         ``doubly linked list */` `        ``while` `(current != ``null``) { ` `            ``temp = current.prev; ` `            ``current.prev = current.next; ` `            ``current.next = temp; ` `            ``current = current.prev; ` `        ``} ` ` `  `        ``/* Before changing head, check for the cases like empty  ` `         ``list and list with only one node */` `        ``if` `(temp != ``null``) { ` `            ``head = temp.prev; ` `        ``} ` `    ``} ` ` `  `    ``/* UTILITY FUNCTIONS */` `    ``/* Function to insert a node at the beginging of the Doubly Linked List */` `    ``void` `push(``int` `new_data) { ` `        ``/* allocate node */` `        ``Node new_node = ``new` `Node(new_data); ` ` `  `        ``/* since we are adding at the begining,  ` `         ``prev is always NULL */` `        ``new_node.prev = ``null``; ` ` `  `        ``/* link the old list off the new node */` `        ``new_node.next = head; ` ` `  `        ``/* change prev of head node to new node */` `        ``if` `(head != ``null``) { ` `            ``head.prev = new_node; ` `        ``} ` ` `  `        ``/* move the head to point to the new node */` `        ``head = new_node; ` `    ``} ` ` `  `    ``/* Function to print nodes in a given doubly linked list  ` `     ``This function is same as printList() of singly linked lsit */` `    ``void` `printList(Node node) { ` `        ``while` `(node != ``null``) { ` `            ``System.out.print(node.data + ``" "``); ` `            ``node = node.next; ` `        ``} ` `    ``} ` ` `  `    ``public` `static` `void` `main(String[] args) { ` `        ``LinkedList list = ``new` `LinkedList(); ` ` `  `        ``/* Let us create a sorted linked list to test the functions ` `         ``Created linked list will be 10->8->4->2 */` `        ``list.push(``2``); ` `        ``list.push(``4``); ` `        ``list.push(``8``); ` `        ``list.push(``10``); ` ` `  `        ``System.out.println(``"Original linked list "``); ` `        ``list.printList(head); ` ` `  `        ``list.reverse(); ` `        ``System.out.println(``""``); ` `        ``System.out.println(``"The reversed Linked List is "``); ` `        ``list.printList(head); ` `    ``} ` `} ` ` `  `// This code has been contributed by Mayank Jaiswal `

## Python

 `# Program to reverse a doubly linked list ` ` `  `# A node of the doublly linked list ` `class` `Node: ` `     `  `    ``# Constructor to create a new node ` `    ``def` `__init__(``self``, data): ` `        ``self``.data ``=` `data  ` `        ``self``.``next` `=` `None` `        ``self``.prev ``=` `None` ` `  `class` `DoublyLinkedList: ` `     ``# Constructor for empty Doubly Linked List ` `    ``def` `__init__(``self``): ` `        ``self``.head ``=` `None` `  `  `    ``# Function reverse a Doubly Linked List ` `    ``def` `reverse(``self``): ` `        ``temp ``=` `None` `        ``current ``=` `self``.head ` `         `  `        ``# Swap next and prev for all nodes of  ` `        ``# doubly linked list ` `        ``while` `current ``is` `not` `None``: ` `            ``temp ``=` `current.prev  ` `            ``current.prev ``=` `current.``next` `            ``current.``next` `=` `temp ` `            ``current ``=` `current.prev ` ` `  `        ``# Before changing head, check for the cases like  ` `        ``# empty list and list with only one node ` `        ``if` `temp ``is` `not` `None``: ` `            ``self``.head ``=` `temp.prev ` `         `  `    ``# 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 ` ` `  ` `  `    ``def` `printList(``self``, node): ` `        ``while``(node ``is` `not` `None``): ` `            ``print` `node.data, ` `            ``node ``=` `node.``next` ` `  `# Driver program to test the above functions ` `dll ``=` `DoublyLinkedList() ` `dll.push(``2``); ` `dll.push(``4``); ` `dll.push(``8``); ` `dll.push(``10``); ` ` `  `print` ```" Original Linked List"``` `dll.printList(dll.head) ` ` `  `# Reverse doubly linked list ` `dll.reverse() ` ` `  `print` ```" Reversed Linked List"``` `dll.printList(dll.head) ` ` `  `# This code is contributed by Nikhil Kumar Singh(nickzuck_007) `

## C#

 `// A C# program to reverse a doubly linked list  ` `using` `System;  ` ` `  `public` `class` `LinkedList ` `{  ` ` `  `    ``static` `Node head;  ` ` `  `    ``class` `Node ` `    ``{  ` ` `  `        ``public` `int` `data;  ` `        ``public` `Node next, prev;  ` ` `  `        ``public` `Node(``int` `d)  ` `        ``{  ` `            ``data = d;  ` `            ``next = prev = ``null``;  ` `        ``}  ` `    ``}  ` ` `  `    ``/* Function to reverse a Doubly Linked List */` `    ``void` `reverse()  ` `    ``{  ` `        ``Node temp = ``null``;  ` `        ``Node current = head;  ` ` `  `        ``/* swap next and prev for all nodes of  ` `        ``doubly linked list */` `        ``while` `(current != ``null``)  ` `        ``{  ` `            ``temp = current.prev;  ` `            ``current.prev = current.next;  ` `            ``current.next = temp;  ` `            ``current = current.prev;  ` `        ``}  ` ` `  `        ``/* Before changing head, check for ` `          ``the cases like empty list and ` `         ``list with only one node */` `        ``if` `(temp != ``null``) ` `        ``{  ` `            ``head = temp.prev;  ` `        ``}  ` `    ``}  ` ` `  `    ``/* UTILITY FUNCTIONS */` `    ``/* Function to insert a node at the  ` `    ``beginging of the Doubly Linked List */` `    ``void` `push(``int` `new_data)  ` `    ``{  ` `         `  `        ``/* allocate node */` `        ``Node new_node = ``new` `Node(new_data);  ` ` `  `        ``/* since we are adding at the begining,  ` `        ``prev is always NULL */` `        ``new_node.prev = ``null``;  ` ` `  `        ``/* link the old list off the new node */` `        ``new_node.next = head;  ` ` `  `        ``/* change prev of head node to new node */` `        ``if` `(head != ``null``)  ` `        ``{  ` `            ``head.prev = new_node;  ` `        ``}  ` ` `  `        ``/* move the head to point to the new node */` `        ``head = new_node;  ` `    ``}  ` ` `  `    ``/* Function to print nodes in a given ` `    ``doubly linked list This function is ` `    ``same as printList() of singly linked lsit */` `    ``void` `printList(Node node)  ` `    ``{  ` `        ``while` `(node != ``null``) ` `        ``{  ` `            ``Console.Write(node.data + ``" "``);  ` `            ``node = node.next;  ` `        ``}  ` `    ``}  ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `Main(String[] args) ` `    ``{  ` `        ``LinkedList list = ``new` `LinkedList();  ` ` `  `        ``/* Let us create a sorted linked list  ` `        ``to test the functions Created linked  ` `        ``list will be 10->8->4->2 */` `        ``list.push(2);  ` `        ``list.push(4);  ` `        ``list.push(8);  ` `        ``list.push(10);  ` ` `  `        ``Console.WriteLine(``"Original linked list "``);  ` `        ``list.printList(head);  ` ` `  `        ``list.reverse();  ` `        ``Console.WriteLine(``""``);  ` `        ``Console.WriteLine(``"The reversed Linked List is "``);  ` `        ``list.printList(head);  ` `    ``}  ` `}  ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```Original linked list
10 8 4 2
The reversed Linked List is
2 4 8 10 ```

Time Complexity: O(n)

We can also swap data instead of pointers to reverse the Doubly Linked List. Method used for reversing array can be used to swap data. Swapping data can be costly compared to pointers if size of data item(s) is more.

Please write comments if you find any of the above codes/algorithms incorrect, or find better ways to solve the same problem.

This article is attributed to GeeksforGeeks.org

## tags:

Linked List doubly linked list Linked List

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