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Swap nodes in a linked list without swapping data
• Difficulty Level : Medium
• Last Updated : 18 May, 2021

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```

This may look a simple problem, but is an interesting question as it has the following cases to be handled.

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

How to write a clean working code that handles all the above possibilities.

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 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 off 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 off 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 ```

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

Simpler 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 therir 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();``}`

## 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 therir 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 therir 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 */`
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 ```