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# Swap nodes in a linked list without swapping data

### Introduction:

A linked list is a data structure that stores a sequence of elements, where each element points to the next element in the sequence. Linked lists consist of nodes, where each node contains both data and a pointer to the next node in the sequence. The first node is called the head node, and the last node is called the tail node. Linked lists are commonly used in programming because they can be dynamically resized and can be used to implement other data structures such as stacks, queues, and hash tables.

1. Dynamic size: Linked lists are dynamic data structures that can be resized during the execution of the program.
2. Easy insertion and deletion: Elements can be inserted or deleted from a linked list easily by adjusting the pointers to the next nodes.
3. Sequential access: Linked lists provide sequential access to elements, which can be useful in some algorithms and data processing.

1. No random access: Linked lists do not allow for random access to elements, meaning that you cannot directly access a specific element in the list without traversing through all the elements before it.
2. Extra memory: Linked lists use extra memory to store the pointers to the next nodes, which can be a disadvantage in memory-constrained environments.
3. Overhead: Linked lists have more overhead than arrays due to the extra memory usage and pointer manipulation.

### Reference book:

“Data Structures and Algorithms in C++” by Michael T. Goodrich, Roberto Tamassia, and David M. Mount. This book covers a wide range of data structures and algorithms, including linked lists, and provides clear explanations and examples in C++.Given a linked list and two keys in it, swap nodes for two given keys. Nodes should be swapped by changing links. Swapping data of nodes may be expensive in many situations when data contains many fields. It may be assumed that all keys in the linked list are distinct.

Examples:

Input: 10->15->12->13->20->14,  x = 12, y = 20
Output: 10->15->20->13->12->14

Input: 10->15->12->13->20->14,  x = 10, y = 20
Output: 20->15->12->13->10->14

Input: 10->15->12->13->20->14,  x = 12, y = 13
Output: 10->15->13->12->20->14

The problem has the following cases to be handled:

• x and y may or may not be adjacent.
• Either x or y may be a head node.
• Either x or y may be the last node.
• x and / or y may not be present in the linked list.

Naive Approach:

The idea is to first search x and y in the given linked list. If any of them is not present, then return. While searching for x and y, keep track of current and previous pointers. First change next of previous pointers, then change next of current pointers.

Below is the diagram of the case where either Node X or Node Y is the head node of the list. Swapping when Node X is the head of the List.

Below is the diagram of the case where Nodes X and Y are both not the head node of the list. Swapping when neither Node X or Node Y is the head of the list.

Below is the implementation of the above approach:

## C++

 `/* This program swaps the nodes of linked list rather``than swapping the field from the nodes.*/``#include ``using` `namespace` `std;` `/* A linked list node */``class` `Node {``public``:``    ``int` `data;``    ``Node* next;``};` `/* Function to swap nodes x and y in linked list by``changing links */``void` `swapNodes(Node** head_ref, ``int` `x, ``int` `y)``{``    ``// Nothing to do if x and y are same``    ``if` `(x == y)``        ``return``;` `    ``// Search for x (keep track of prevX and CurrX``    ``Node *prevX = NULL, *currX = *head_ref;``    ``while` `(currX && currX->data != x) {``        ``prevX = currX;``        ``currX = currX->next;``    ``}` `    ``// Search for y (keep track of prevY and CurrY``    ``Node *prevY = NULL, *currY = *head_ref;``    ``while` `(currY && currY->data != y) {``        ``prevY = currY;``        ``currY = currY->next;``    ``}` `    ``// If either x or y is not present, nothing to do``    ``if` `(currX == NULL || currY == NULL)``        ``return``;` `    ``// If x is not head of linked list``    ``if` `(prevX != NULL)``        ``prevX->next = currY;``    ``else` `// Else make y as new head``        ``*head_ref = currY;` `    ``// If y is not head of linked list``    ``if` `(prevY != NULL)``        ``prevY->next = currX;``    ``else` `// Else make x as new head``        ``*head_ref = currX;` `    ``// Swap next pointers``    ``Node* temp = currY->next;``    ``currY->next = currX->next;``    ``currX->next = temp;``}` `/* Function to add a node at the beginning of 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;` `    ``/* link the old list of the new node */``    ``new_node->next = (*head_ref);` `    ``/* move the head to point to the new node */``    ``(*head_ref) = new_node;``}` `/* Function to print nodes in a given linked list */``void` `printList(Node* node)``{``    ``while` `(node != NULL) {``        ``cout << node->data << ``" "``;``        ``node = node->next;``    ``}``}` `/* Driver program to test above function */``int` `main()``{``    ``Node* start = NULL;` `    ``/* The constructed linked list is:``    ``1->2->3->4->5->6->7 */``    ``push(&start, 7);``    ``push(&start, 6);``    ``push(&start, 5);``    ``push(&start, 4);``    ``push(&start, 3);``    ``push(&start, 2);``    ``push(&start, 1);` `    ``cout << ``"Linked list before calling swapNodes() "``;``    ``printList(start);` `    ``swapNodes(&start, 4, 3);` `    ``cout << ``"\nLinked list after calling swapNodes() "``;``    ``printList(start);` `    ``return` `0;``}` `// This is code is contributed by rathbhupendra`

## C

 `/* This program swaps the nodes of linked list rather``   ``than swapping the field from the nodes.*/` `#include ``#include ` `/* A linked list node */``struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};` `/* Function to swap nodes x and y in linked list by``   ``changing links */``void` `swapNodes(``struct` `Node** head_ref, ``int` `x, ``int` `y)``{``    ``// Nothing to do if x and y are same``    ``if` `(x == y)``        ``return``;` `    ``// Search for x (keep track of prevX and CurrX``    ``struct` `Node *prevX = NULL, *currX = *head_ref;``    ``while` `(currX && currX->data != x) {``        ``prevX = currX;``        ``currX = currX->next;``    ``}` `    ``// Search for y (keep track of prevY and CurrY``    ``struct` `Node *prevY = NULL, *currY = *head_ref;``    ``while` `(currY && currY->data != y) {``        ``prevY = currY;``        ``currY = currY->next;``    ``}` `    ``// If either x or y is not present, nothing to do``    ``if` `(currX == NULL || currY == NULL)``        ``return``;` `    ``// If x is not head of linked list``    ``if` `(prevX != NULL)``        ``prevX->next = currY;``    ``else` `// Else make y as new head``        ``*head_ref = currY;` `    ``// If y is not head of linked list``    ``if` `(prevY != NULL)``        ``prevY->next = currX;``    ``else` `// Else make x as new head``        ``*head_ref = currX;` `    ``// Swap next pointers``    ``struct` `Node* temp = currY->next;``    ``currY->next = currX->next;``    ``currX->next = temp;``}` `/* Function to add a node at the beginning of 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;` `    ``/* link the old list of the new node */``    ``new_node->next = (*head_ref);` `    ``/* move the head to point to the new node */``    ``(*head_ref) = new_node;``}` `/* Function to print nodes in a given linked list */``void` `printList(``struct` `Node* node)``{``    ``while` `(node != NULL) {``        ``printf``(``"%d "``, node->data);``        ``node = node->next;``    ``}``}` `/* Driver program to test above function */``int` `main()``{``    ``struct` `Node* start = NULL;` `    ``/* The constructed linked list is:``     ``1->2->3->4->5->6->7 */``    ``push(&start, 7);``    ``push(&start, 6);``    ``push(&start, 5);``    ``push(&start, 4);``    ``push(&start, 3);``    ``push(&start, 2);``    ``push(&start, 1);` `    ``printf``(``"\n Linked list before calling swapNodes() "``);``    ``printList(start);` `    ``swapNodes(&start, 4, 3);` `    ``printf``(``"\n Linked list after calling swapNodes() "``);``    ``printList(start);` `    ``return` `0;``}`

## Java

 `// Java program to swap two given nodes of a linked list` `class` `Node {``    ``int` `data;``    ``Node next;``    ``Node(``int` `d)``    ``{``        ``data = d;``        ``next = ``null``;``    ``}``}` `class` `LinkedList {``    ``Node head; ``// head of list` `    ``/* Function to swap Nodes x and y in linked list by``       ``changing links */``    ``public` `void` `swapNodes(``int` `x, ``int` `y)``    ``{``        ``// Nothing to do if x and y are same``        ``if` `(x == y)``            ``return``;` `        ``// Search for x (keep track of prevX and CurrX)``        ``Node prevX = ``null``, currX = head;``        ``while` `(currX != ``null` `&& currX.data != x) {``            ``prevX = currX;``            ``currX = currX.next;``        ``}` `        ``// Search for y (keep track of prevY and currY)``        ``Node prevY = ``null``, currY = head;``        ``while` `(currY != ``null` `&& currY.data != y) {``            ``prevY = currY;``            ``currY = currY.next;``        ``}` `        ``// If either x or y is not present, nothing to do``        ``if` `(currX == ``null` `|| currY == ``null``)``            ``return``;` `        ``// If x is not head of linked list``        ``if` `(prevX != ``null``)``            ``prevX.next = currY;``        ``else` `// make y the new head``            ``head = currY;` `        ``// If y is not head of linked list``        ``if` `(prevY != ``null``)``            ``prevY.next = currX;``        ``else` `// make x the new head``            ``head = currX;` `        ``// Swap next pointers``        ``Node temp = currX.next;``        ``currX.next = currY.next;``        ``currY.next = temp;``    ``}` `    ``/* Function to add Node at beginning of list. */``    ``public` `void` `push(``int` `new_data)``    ``{``        ``/* 1. alloc the Node and put the data */``        ``Node new_Node = ``new` `Node(new_data);` `        ``/* 2. Make next of new Node as head */``        ``new_Node.next = head;` `        ``/* 3. Move the head to point to new Node */``        ``head = new_Node;``    ``}` `    ``/* This function prints contents of linked list starting``       ``from the given Node */``    ``public` `void` `printList()``    ``{``        ``Node tNode = head;``        ``while` `(tNode != ``null``) {``            ``System.out.print(tNode.data + ``" "``);``            ``tNode = tNode.next;``        ``}``    ``}` `    ``/* Driver program to test above function */``    ``public` `static` `void` `main(String[] args)``    ``{``        ``LinkedList llist = ``new` `LinkedList();` `        ``/* The constructed linked list is:``            ``1->2->3->4->5->6->7 */``        ``llist.push(``7``);``        ``llist.push(``6``);``        ``llist.push(``5``);``        ``llist.push(``4``);``        ``llist.push(``3``);``        ``llist.push(``2``);``        ``llist.push(``1``);` `        ``System.out.print(``            ``"\n Linked list before calling swapNodes() "``);``        ``llist.printList();` `        ``llist.swapNodes(``4``, ``3``);` `        ``System.out.print(``            ``"\n Linked list after calling swapNodes() "``);``        ``llist.printList();``    ``}``}``// This code is contributed by Rajat Mishra`

## Python

 `# Python program to swap two given nodes of a linked list``class` `LinkedList(``object``):``    ``def` `__init__(``self``):``        ``self``.head ``=` `None` `    ``# head of list``    ``class` `Node(``object``):``        ``def` `__init__(``self``, d):``            ``self``.data ``=` `d``            ``self``.``next` `=` `None` `    ``# Function to swap Nodes x and y in linked list by``    ``# changing links``    ``def` `swapNodes(``self``, x, y):` `        ``# Nothing to do if x and y are same``        ``if` `x ``=``=` `y:``            ``return` `        ``# Search for x (keep track of prevX and CurrX)``        ``prevX ``=` `None``        ``currX ``=` `self``.head``        ``while` `currX !``=` `None` `and` `currX.data !``=` `x:``            ``prevX ``=` `currX``            ``currX ``=` `currX.``next` `        ``# Search for y (keep track of prevY and currY)``        ``prevY ``=` `None``        ``currY ``=` `self``.head``        ``while` `currY !``=` `None` `and` `currY.data !``=` `y:``            ``prevY ``=` `currY``            ``currY ``=` `currY.``next` `        ``# If either x or y is not present, nothing to do``        ``if` `currX ``=``=` `None` `or` `currY ``=``=` `None``:``            ``return``        ``# If x is not head of linked list``        ``if` `prevX !``=` `None``:``            ``prevX.``next` `=` `currY``        ``else``:  ``# make y the new head``            ``self``.head ``=` `currY` `        ``# If y is not head of linked list``        ``if` `prevY !``=` `None``:``            ``prevY.``next` `=` `currX``        ``else``:  ``# make x the new head``            ``self``.head ``=` `currX` `        ``# Swap next pointers``        ``temp ``=` `currX.``next``        ``currX.``next` `=` `currY.``next``        ``currY.``next` `=` `temp` `    ``# Function to add Node at beginning of list.``    ``def` `push(``self``, new_data):` `        ``# 1. alloc the Node and put the data``        ``new_Node ``=` `self``.Node(new_data)` `        ``# 2. Make next of new Node as head``        ``new_Node.``next` `=` `self``.head` `        ``# 3. Move the head to point to new Node``        ``self``.head ``=` `new_Node` `    ``# This function prints contents of linked list starting``    ``# from the given Node``    ``def` `printList(``self``):``        ``tNode ``=` `self``.head``        ``while` `tNode !``=` `None``:``            ``print` `tNode.data,``            ``tNode ``=` `tNode.``next`  `# Driver program to test above function``llist ``=` `LinkedList()` `# The constructed linked list is:``# 1->2->3->4->5->6->7``llist.push(``7``)``llist.push(``6``)``llist.push(``5``)``llist.push(``4``)``llist.push(``3``)``llist.push(``2``)``llist.push(``1``)``print` `"Linked list before calling swapNodes() "``llist.printList()``llist.swapNodes(``4``, ``3``)``print` `"\nLinked list after calling swapNodes() "``llist.printList()` `# This code is contributed by BHAVYA JAIN`

## C#

 `// C# program to swap two given``// nodes of a linked list``using` `System;` `class` `Node {``    ``public` `int` `data;``    ``public` `Node next;``    ``public` `Node(``int` `d)``    ``{``        ``data = d;``        ``next = ``null``;``    ``}``}` `public` `class` `LinkedList {``    ``Node head; ``// head of list` `    ``/* Function to swap Nodes x and y in``    ``linked list by changing links */``    ``public` `void` `swapNodes(``int` `x, ``int` `y)``    ``{``        ``// Nothing to do if x and y are same``        ``if` `(x == y)``            ``return``;` `        ``// Search for x (keep track of prevX and CurrX)``        ``Node prevX = ``null``, currX = head;``        ``while` `(currX != ``null` `&& currX.data != x) {``            ``prevX = currX;``            ``currX = currX.next;``        ``}` `        ``// Search for y (keep track of prevY and currY)``        ``Node prevY = ``null``, currY = head;``        ``while` `(currY != ``null` `&& currY.data != y) {``            ``prevY = currY;``            ``currY = currY.next;``        ``}` `        ``// If either x or y is not present, nothing to do``        ``if` `(currX == ``null` `|| currY == ``null``)``            ``return``;` `        ``// If x is not head of linked list``        ``if` `(prevX != ``null``)``            ``prevX.next = currY;``        ``else` `// make y the new head``            ``head = currY;` `        ``// If y is not head of linked list``        ``if` `(prevY != ``null``)``            ``prevY.next = currX;``        ``else` `// make x the new head``            ``head = currX;` `        ``// Swap next pointers``        ``Node temp = currX.next;``        ``currX.next = currY.next;``        ``currY.next = temp;``    ``}` `    ``/* Function to add Node at beginning of list. */``    ``public` `void` `push(``int` `new_data)``    ``{``        ``/* 1. alloc the Node and put the data */``        ``Node new_Node = ``new` `Node(new_data);` `        ``/* 2. Make next of new Node as head */``        ``new_Node.next = head;` `        ``/* 3. Move the head to point to new Node */``        ``head = new_Node;``    ``}` `    ``/* This function prints contents of linked list``    ``starting from the given Node */``    ``public` `void` `printList()``    ``{``        ``Node tNode = head;``        ``while` `(tNode != ``null``) {``            ``Console.Write(tNode.data + ``" "``);``            ``tNode = tNode.next;``        ``}``    ``}` `    ``/* Driver code */``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``LinkedList llist = ``new` `LinkedList();` `        ``/* The constructed linked list is:``            ``1->2->3->4->5->6->7 */``        ``llist.push(7);``        ``llist.push(6);``        ``llist.push(5);``        ``llist.push(4);``        ``llist.push(3);``        ``llist.push(2);``        ``llist.push(1);` `        ``Console.Write(``            ``"\n Linked list before calling swapNodes() "``);``        ``llist.printList();` `        ``llist.swapNodes(4, 3);` `        ``Console.Write(``            ``"\n Linked list after calling swapNodes() "``);``        ``llist.printList();``    ``}``}` `// This code is contributed by 29AjayKumar`

## Javascript

 ``

Output

```Linked list before calling swapNodes() 1 2 3 4 5 6 7
Linked list after calling swapNodes() 1 2 4 3 5 6 7 ```

Time Complexity: O(N)
Auxiliary Space: O(1)

Efficient Approach:

The above code can be optimized to search x and y in a single traversal. Two loops are used to keep the program simple.

Below is the implementation of the above approach:

## C++

 `// C++ program to swap two given nodes of a linked list``#include ``using` `namespace` `std;` `// A linked list node class``class` `Node {``public``:``    ``int` `data;``    ``class` `Node* next;``    ``// constructor``    ``Node(``int` `val, Node* next)``        ``: data(val)``        ``, next(next)``    ``{``    ``}``    ``// print list from this to last till null``    ``void` `printList()``    ``{``        ``Node* node = ``this``;``        ``while` `(node != NULL) {``            ``cout << node->data << ``" "``;``            ``node = node->next;``        ``}``        ``cout << endl;``    ``}``};` `// Function to add a node at the beginning of List``void` `push(Node** head_ref, ``int` `new_data)``{``    ``// allocate node``    ``(*head_ref) = ``new` `Node(new_data, *head_ref);``}` `void` `swap(Node*& a, Node*& b)``{``    ``Node* temp = a;``    ``a = b;``    ``b = temp;``}` `void` `swapNodes(Node** head_ref, ``int` `x, ``int` `y)``{``    ``// Nothing to do if x and y are same``    ``if` `(x == y)``        ``return``;``    ``Node **a = NULL, **b = NULL;``    ``// search for x and y in the linked list``    ``// and store their pointer in a and b``    ``while` `(*head_ref) {``        ``if` `((*head_ref)->data == x)``            ``a = head_ref;``        ``else` `if` `((*head_ref)->data == y)``            ``b = head_ref;``        ``head_ref = &((*head_ref)->next);``    ``}``    ``// if we have found both a and b``    ``// in the linked list swap current``    ``// pointer and next pointer of these``    ``if` `(a && b) {``        ``swap(*a, *b);``        ``swap(((*a)->next), ((*b)->next));``    ``}``}` `// Driver code``int` `main()``{``    ``Node* start = NULL;``    ``// The constructed linked list is:``    ``// 1->2->3->4->5->6->7``    ``push(&start, 7);``    ``push(&start, 6);``    ``push(&start, 5);``    ``push(&start, 4);``    ``push(&start, 3);``    ``push(&start, 2);``    ``push(&start, 1);` `    ``cout << ``"Linked list before calling swapNodes() "``;``    ``start->printList();` `    ``swapNodes(&start, 6, 1);` `    ``cout << ``"Linked list after calling swapNodes() "``;``    ``start->printList();``}` `// This code is contributed by Sania Kumari Gupta``// (kriSania804)`

## C

 `// C program to swap two given nodes of a linked list``#include ``#include ` `/* A linked list node */``typedef` `struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``} Node;` `/* Function to add a node at the beginning of List */``void` `push(``struct` `Node** head_ref, ``int` `new_data)``{``    ``/* allocate node */``    ``Node* new_node = (Node*)``malloc``(``sizeof``(``struct` `Node));``    ``/* put in the data  */``    ``new_node->data = new_data;``    ``/* link the old list of the new node */``    ``new_node->next = (*head_ref);``    ``/* move the head to point to the new node */``    ``(*head_ref) = new_node;``}` `/* Function to print nodes in a given linked list */``void` `printList(Node* node)``{``    ``while` `(node != NULL) {``        ``printf``(``"%d "``, node->data);``        ``node = node->next;``    ``}``}` `void` `swap(Node* a, Node* b)``{``    ``Node temp = *a;``    ``*a = *b;``    ``*b = temp;``}` `void` `swapNodes(Node** head_ref, ``int` `x, ``int` `y)``{``    ``// Nothing to do if x and y are same``    ``if` `(x == y)``        ``return``;``    ``Node **a = NULL, **b = NULL;``    ``// search for x and y in the linked list``    ``// and store their pointer in a and b``    ``while` `(*head_ref) {``        ``if` `((*head_ref)->data == x)``            ``a = head_ref;``        ``else` `if` `((*head_ref)->data == y)``            ``b = head_ref;``        ``head_ref = &((*head_ref)->next);``    ``}``    ``// if we have found both a and b in the linked list swap``    ``// current pointer and next pointer of these``    ``if` `(a && b) {``        ``swap(*a, *b);``        ``swap(((*a)->next), ((*b)->next));``    ``}``}` `// Driver code``int` `main()``{``    ``struct` `Node* start = NULL;``    ``/* The constructed linked list is:``     ``1->2->3->4->5->6->7 */``    ``push(&start, 7);``    ``push(&start, 6);``    ``push(&start, 5);``    ``push(&start, 4);``    ``push(&start, 3);``    ``push(&start, 2);``    ``push(&start, 1);` `    ``printf``(``"Linked list before calling swapNodes() "``);``    ``printList(start);``    ``printf``(``"\n"``);` `    ``swapNodes(&start, 6, 1);` `    ``printf``(``"Linked list after calling swapNodes() "``);``    ``printList(start);``}` `// This code is contributed by Sania Kumari Gupta``// (kriSania804)`

## Java

 `// Java program to swap two given nodes of a linked list``public` `class` `Solution {` `    ``// Represent a node of the singly linked list``    ``class` `Node {``        ``int` `data;``        ``Node next;` `        ``public` `Node(``int` `data)``        ``{``            ``this``.data = data;``            ``this``.next = ``null``;``        ``}``    ``}` `    ``// Represent the head and tail of the singly linked list``    ``public` `Node head = ``null``;``    ``public` `Node tail = ``null``;` `    ``// addNode() will add a new node to the list``    ``public` `void` `addNode(``int` `data)``    ``{``        ``// Create a new node``        ``Node newNode = ``new` `Node(data);` `        ``// Checks if the list is empty``        ``if` `(head == ``null``) {``            ``// If list is empty, both head and``            ``// tail will point to new node``            ``head = newNode;``            ``tail = newNode;``        ``}``        ``else` `{``            ``// newNode will be added after tail such that``            ``// tail's next will point to newNode``            ``tail.next = newNode;``            ``// newNode will become new tail of the list``            ``tail = newNode;``        ``}``    ``}` `    ``// swap() will swap the given two nodes``    ``public` `void` `swap(``int` `n1, ``int` `n2)``    ``{``        ``Node prevNode1 = ``null``, prevNode2 = ``null``,``             ``node1 = head, node2 = head;` `        ``// Checks if list is empty``        ``if` `(head == ``null``) {``            ``return``;``        ``}` `        ``// If n1 and n2 are equal, then``        ``// list will remain the same``        ``if` `(n1 == n2)``            ``return``;` `        ``// Search for node1``        ``while` `(node1 != ``null` `&& node1.data != n1) {``            ``prevNode1 = node1;``            ``node1 = node1.next;``        ``}` `        ``// Search for node2``        ``while` `(node2 != ``null` `&& node2.data != n2) {``            ``prevNode2 = node2;``            ``node2 = node2.next;``        ``}` `        ``if` `(node1 != ``null` `&& node2 != ``null``) {` `            ``// If previous node to node1 is not null then,``            ``// it will point to node2``            ``if` `(prevNode1 != ``null``)``                ``prevNode1.next = node2;``            ``else``                ``head = node2;` `            ``// If previous node to node2 is not null then,``            ``// it will point to node1``            ``if` `(prevNode2 != ``null``)``                ``prevNode2.next = node1;``            ``else``                ``head = node1;` `            ``// Swaps the next nodes of node1 and node2``            ``Node temp = node1.next;``            ``node1.next = node2.next;``            ``node2.next = temp;``        ``}``        ``else` `{``            ``System.out.println(``"Swapping is not possible"``);``        ``}``    ``}` `    ``// display() will display all the``    ``// nodes present in the list``    ``public` `void` `display()``    ``{``        ``// Node current will point to head``        ``Node current = head;` `        ``if` `(head == ``null``) {``            ``System.out.println(``"List is empty"``);``            ``return``;``        ``}``        ``while` `(current != ``null``) {``            ``// Prints each node by incrementing pointer``            ``System.out.print(current.data + ``" "``);``            ``current = current.next;``        ``}``        ``System.out.println();``    ``}` `    ``public` `static` `void` `main(String[] args)``    ``{` `        ``Solution sList = ``new` `Solution();` `        ``// Add nodes to the list``        ``sList.addNode(``1``);``        ``sList.addNode(``2``);``        ``sList.addNode(``3``);``        ``sList.addNode(``4``);``        ``sList.addNode(``5``);``        ``sList.addNode(``6``);``        ``sList.addNode(``7``);` `        ``System.out.println(``"Original list: "``);``        ``sList.display();` `        ``// Swaps the node 2 with node 5``        ``sList.swap(``6``, ``1``);` `        ``System.out.println(``"List after swapping nodes: "``);``        ``sList.display();``    ``}``}`

## Python3

 `# Python3 program to swap two given``# nodes of a linked list` `# A linked list node class`  `class` `Node:` `    ``# constructor``    ``def` `__init__(``self``, val``=``None``, next1``=``None``):``        ``self``.data ``=` `val``        ``self``.``next` `=` `next1` `    ``# print list from this``    ``# to last till None``    ``def` `printList(``self``):` `        ``node ``=` `self` `        ``while` `(node !``=` `None``):``            ``print``(node.data, end``=``" "``)``            ``node ``=` `node.``next``        ``print``(``" "``)` `# Function to add a node``# at the beginning of List`  `def` `push(head_ref, new_data):` `    ``# allocate node``    ``(head_ref) ``=` `Node(new_data, head_ref)``    ``return` `head_ref`  `def` `swapNodes(head_ref, x, y):``    ``head ``=` `head_ref` `    ``# Nothing to do if x and y are same``    ``if` `(x ``=``=` `y):``        ``return` `None` `    ``a ``=` `None``    ``b ``=` `None` `    ``# search for x and y in the linked list``    ``# and store their pointer in a and b``    ``while` `(head_ref.``next` `!``=` `None``):` `        ``if` `((head_ref.``next``).data ``=``=` `x):``            ``a ``=` `head_ref` `        ``elif` `((head_ref.``next``).data ``=``=` `y):``            ``b ``=` `head_ref` `        ``head_ref ``=` `((head_ref).``next``)` `    ``# if we have found both a and b``    ``# in the linked list swap current``    ``# pointer and next pointer of these``    ``if` `(a !``=` `None` `and` `b !``=` `None``):``        ``temp ``=` `a.``next``        ``a.``next` `=` `b.``next``        ``b.``next` `=` `temp``        ``temp ``=` `a.``next``.``next``        ``a.``next``.``next` `=` `b.``next``.``next``        ``b.``next``.``next` `=` `temp` `    ``return` `head` `# Driver code`  `start ``=` `None` `# The constructed linked list is:``# 1.2.3.4.5.6.7``start ``=` `push(start, ``7``)``start ``=` `push(start, ``6``)``start ``=` `push(start, ``5``)``start ``=` `push(start, ``4``)``start ``=` `push(start, ``3``)``start ``=` `push(start, ``2``)``start ``=` `push(start, ``1``)` `print``(``"Linked list before calling swapNodes() "``)``start.printList()` `start ``=` `swapNodes(start, ``6``, ``1``)` `print``(``"Linked list after calling swapNodes() "``)``start.printList()` `# This code is contributed by Arnab Kundu`

## C#

 `// C# program to swap two``// given nodes of a linked list``using` `System;` `class` `GFG {``    ``// A linked list node class``    ``public` `class` `Node {` `        ``public` `int` `data;``        ``public` `Node next;` `        ``// constructor``        ``public` `Node(``int` `val, Node next1)``        ``{``            ``data = val;``            ``next = next1;``        ``}` `        ``// print list from this``        ``// to last till null``        ``public` `void` `printList()``        ``{` `            ``Node node = ``this``;` `            ``while` `(node != ``null``) {``                ``Console.Write(node.data + ``" "``);``                ``node = node.next;``            ``}``            ``Console.WriteLine();``        ``}``    ``}` `    ``// Function to add a node``    ``// at the beginning of List``    ``static` `Node push(Node head_ref, ``int` `new_data)``    ``{` `        ``// allocate node``        ``(head_ref) = ``new` `Node(new_data, head_ref);``        ``return` `head_ref;``    ``}` `    ``static` `Node swapNodes(Node head_ref, ``int` `x, ``int` `y)``    ``{``        ``Node head = head_ref;` `        ``// Nothing to do if x and y are same``        ``if` `(x == y)``            ``return` `null``;` `        ``Node a = ``null``, b = ``null``;` `        ``// search for x and y in the linked list``        ``// and store their pointer in a and b``        ``while` `(head_ref.next != ``null``) {` `            ``if` `((head_ref.next).data == x) {``                ``a = head_ref;``            ``}` `            ``else` `if` `((head_ref.next).data == y) {``                ``b = head_ref;``            ``}` `            ``head_ref = ((head_ref).next);``        ``}` `        ``// if we have found both a and b``        ``// in the linked list swap current``        ``// pointer and next pointer of these``        ``if` `(a != ``null` `&& b != ``null``) {``            ``Node temp = a.next;``            ``a.next = b.next;``            ``b.next = temp;``            ``temp = a.next.next;``            ``a.next.next = b.next.next;``            ``b.next.next = temp;``        ``}``        ``return` `head;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{` `        ``Node start = ``null``;` `        ``// The constructed linked list is:``        ``// 1.2.3.4.5.6.7``        ``start = push(start, 7);``        ``start = push(start, 6);``        ``start = push(start, 5);``        ``start = push(start, 4);``        ``start = push(start, 3);``        ``start = push(start, 2);``        ``start = push(start, 1);` `        ``Console.Write(``            ``"Linked list before calling swapNodes() "``);``        ``start.printList();` `        ``start = swapNodes(start, 6, 1);` `        ``Console.Write(``            ``"Linked list after calling swapNodes() "``);``        ``start.printList();``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``

Output

```Linked list before calling swapNodes() 1 2 3 4 5 6 7
Linked list after calling swapNodes() 6 2 3 4 5 1 7 ```

Time complexity: O(N)
Auxiliary Space: O(1)

### To swap nodes in a linked list without swapping data, you need to change the pointers of the nodes that come before the two nodes you want to swap. Here’s an example function that swaps two nodes in a linked list:

void swap_nodes(Node** head_ref, Node* node1, Node* node2) {
// if the two nodes are the same, no swapping is necessary
if (node1 == node2) {
return;
}

// find the node that comes before node1
Node* prev1 = NULL;
while (current_node != NULL && current_node != node1) {
prev1 = current_node;
current_node = current_node->next;
}

// find the node that comes before node2
Node* prev2 = NULL;
while (current_node != NULL && current_node != node2) {
prev2 = current_node;
current_node = current_node->next;
}

// if either node1 or node2 is not in the list, no swapping is necessary
if (current_node == NULL) {
return;
}

// if node1 is the head of the list, update the head pointer
if (prev1 == NULL) {
} else {
prev1->next = node2;
}

// if node2 is the head of the list, update the head pointer
if (prev2 == NULL) {
} else {
prev2->next = node1;
}

// swap the next pointers of node1 and node2
Node* temp = node1->next;
node1->next = node2->next;
node2->next = temp;
}

Sure, here’s the code for swapping nodes in a linked list without swapping data in C++, Java, and Python, along with their corresponding outputs.

## C++

 `#include ` `using` `namespace` `std;` `class` `Node {``public``:``    ``int` `data;``    ``Node* next;` `    ``Node(``int` `data) {``        ``this``->data = data;``        ``this``->next = nullptr;``    ``}``};` `void` `print_list(Node* head) {``    ``while` `(head != nullptr) {``        ``cout << head->data << ``" "``;``        ``head = head->next;``    ``}``    ``cout << endl;``}` `void` `swap_nodes(Node** head_ref, Node* node1, Node* node2) {``    ``if` `(node1 == node2) {``        ``return``;``    ``}` `    ``Node* prev1 = nullptr;``    ``Node* current_node = *head_ref;``    ``while` `(current_node != nullptr && current_node != node1) {``        ``prev1 = current_node;``        ``current_node = current_node->next;``    ``}` `    ``Node* prev2 = nullptr;``    ``current_node = *head_ref;``    ``while` `(current_node != nullptr && current_node != node2) {``        ``prev2 = current_node;``        ``current_node = current_node->next;``    ``}` `    ``if` `(current_node == nullptr) {``        ``return``;``    ``}` `    ``if` `(prev1 == nullptr) {``        ``*head_ref = node2;``    ``} ``else` `{``        ``prev1->next = node2;``    ``}` `    ``if` `(prev2 == nullptr) {``        ``*head_ref = node1;``    ``} ``else` `{``        ``prev2->next = node1;``    ``}` `    ``Node* temp = node1->next;``    ``node1->next = node2->next;``    ``node2->next = temp;``}` `int` `main() {``    ``Node* head = ``new` `Node(1);``    ``head->next = ``new` `Node(2);``    ``head->next->next = ``new` `Node(3);``    ``head->next->next->next = ``new` `Node(4);``    ``head->next->next->next->next = ``new` `Node(5);` `    ``cout << ``"Original list: "``;``    ``print_list(head);` `    ``swap_nodes(&head, head->next, head->next->next);` `    ``cout << ``"Swapped list: "``;``    ``print_list(head);` `    ``return` `0;``}`

## Java

 `public` `class` `LinkedList {``    ``Node head;` `    ``static` `class` `Node {``        ``int` `data;``        ``Node next;` `        ``Node(``int` `data) {``            ``this``.data = data;``            ``this``.next = ``null``;``        ``}``    ``}` `    ``void` `printList() {``        ``Node currentNode = head;``        ``while` `(currentNode != ``null``) {``            ``System.out.print(currentNode.data + ``" "``);``            ``currentNode = currentNode.next;``        ``}``        ``System.out.println();``    ``}` `    ``void` `swapNodes(Node node1, Node node2) {``        ``if` `(node1 == node2) {``            ``return``;``        ``}` `        ``Node prev1 = ``null``;``        ``Node current = head;``        ``while` `(current != ``null` `&& current != node1) {``            ``prev1 = current;``            ``current = current.next;``        ``}` `        ``Node prev2 = ``null``;``        ``current = head;``        ``while` `(current != ``null` `&& current != node2) {``            ``prev2 = current;``            ``current = current.next;``        ``}` `        ``if` `(current == ``null``) {``            ``return``;``        ``}` `        ``if` `(prev1 == ``null``) {``            ``head = node2;``        ``} ``else` `{``            ``prev1.next = node2;``        ``}` `        ``if` `(prev2 == ``null``) {``            ``head = node1;``        ``} ``else` `{``            ``prev2.next = node1;``        ``}` `        ``Node temp = node1.next;``        ``node1.next = node2.next;``        ``node2.next = temp;``    ``}` `    ``public` `static` `void` `main(String[] args) {``        ``LinkedList list = ``new` `LinkedList();``        ``list.head = ``new` `Node(``1``);``        ``list.head.next = ``new` `Node(``2``);``        ``list.head.next.next = ``new` `Node(``3``);``        ``list.head.next.next.next = ``new` `Node(``4``);``        ``list.head.next.next.next.next = ``new` `Node(``5``);` `        ``System.out.print(``"Original list: "``);``        ``list.printList();` `        ``list.swapNodes(list.head.next, list.head.next.next);` `        ``System.out.print(``"Swapped list: "``);``        ``list.printList();``    ``}``}`

## Python3

 `class` `Node:``    ``def` `__init__(``self``, data):``        ``# Initialize the node with data and next pointer``        ``self``.data ``=` `data``        ``self``.``next` `=` `None`  `def` `print_list(head):``    ``# Print the linked list``    ``while` `head !``=` `None``:``        ``print``(head.data, end``=``" "``)``        ``head ``=` `head.``next``    ``print``()`  `def` `swap_nodes(head_ref, node1, node2):``    ``# Swap two nodes in a linked list``    ``if` `node1 ``=``=` `node2:``        ``return` `    ``# Find the previous node of node1``    ``prev1 ``=` `None``    ``current_node ``=` `head_ref[``0``]``    ``while` `current_node !``=` `None` `and` `current_node !``=` `node1:``        ``prev1 ``=` `current_node``        ``current_node ``=` `current_node.``next` `    ``# Find the previous node of node2``    ``prev2 ``=` `None``    ``current_node ``=` `head_ref[``0``]``    ``while` `current_node !``=` `None` `and` `current_node !``=` `node2:``        ``prev2 ``=` `current_node``        ``current_node ``=` `current_node.``next` `    ``if` `current_node ``=``=` `None``:``        ``return` `    ``# Update the next pointer of previous nodes``    ``if` `prev1 ``=``=` `None``:``        ``head_ref[``0``] ``=` `node2``    ``else``:``        ``prev1.``next` `=` `node2` `    ``if` `prev2 ``=``=` `None``:``        ``head_ref[``0``] ``=` `node1``    ``else``:``        ``prev2.``next` `=` `node1` `    ``# Swap the next pointers of the two nodes``    ``temp ``=` `node1.``next``    ``node1.``next` `=` `node2.``next``    ``node2.``next` `=` `temp`  `head ``=` `Node(``1``)``head.``next` `=` `Node(``2``)``head.``next``.``next` `=` `Node(``3``)``head.``next``.``next``.``next` `=` `Node(``4``)``head.``next``.``next``.``next``.``next` `=` `Node(``5``)` `print``(``"Original list: "``)``print_list(head)` `swap_nodes([head], head.``next``, head.``next``.``next``)` `print``(``"Swapped list: "``)``print_list(head)`

## Javascript

 `class Node {``    ``constructor(data) {``        ``// Initialize the node with data and next pointer``        ``this``.data = data;``        ``this``.next = ``null``;``    ``}``}` `function` `print_list(head) {``    ``// Print the linked list``    ``while` `(head != ``null``) {``        ``console.log(head.data + ``" "``);``        ``head = head.next;``    ``}``    ``console.log();``}` `function` `swap_nodes(head_ref, node1, node2) {``    ``// Swap two nodes in a linked list``    ``if` `(node1 == node2) {``        ``return``;``    ``}` `    ``// Find the previous node of node1``    ``let prev1 = ``null``;``    ``let current_node = head_ref;``    ``while` `(current_node != ``null` `&& current_node != node1) {``        ``prev1 = current_node;``        ``current_node = current_node.next;``    ``}` `    ``// Find the previous node of node2``    ``let prev2 = ``null``;``    ``current_node = head_ref;``    ``while` `(current_node != ``null` `&& current_node != node2) {``        ``prev2 = current_node;``        ``current_node = current_node.next;``    ``}` `    ``if` `(current_node == ``null``) {``        ``return``;``    ``}` `    ``// Update the next pointer of previous nodes``    ``if` `(prev1 == ``null``) {``        ``head_ref = node2;``    ``}``    ``else` `{``        ``prev1.next = node2;``    ``}` `    ``if` `(prev2 == ``null``) {``        ``head_ref = node1;``    ``}``    ``else` `{``        ``prev2.next = node1;``    ``}` `    ``// Swap the next pointers of the two nodes``    ``let temp = node1.next;``    ``node1.next = node2.next;``    ``node2.next = temp;``}` `let head = ``new` `Node(1);``head.next = ``new` `Node(2);``head.next.next = ``new` `Node(3);``head.next.next.next = ``new` `Node(4);``head.next.next.next.next = ``new` `Node(5);` `console.log(``"Original list: "``);``print_list(head);` `swap_nodes([head], head.next, head.next.next);` `console.log(``"Swapped list: "``);``print_list(head);`

Output

```Original list: 1 2 3 4 5
Swapped list: 1 3 2 4 5 ```