# Rotate a Linked List

• Difficulty Level : Easy
• Last Updated : 20 Sep, 2022

Given a singly linked list, The task is to rotate the linked list counter-clockwise by k nodes.

Examples:

Input: linked list = 10->20->30->40->50->60, k = 4
Output: 50->60->10->20->30->40.
Explanation: k is smaller than the count of nodes in a linked list so (k+1 )th node i.e. 50 becomes the head node and 60’s next points to 10

Input: linked list = 30->40->50->60, k = 2
Output: 50->60->30->40.

Recommended Practice

Approach: Below is the idea to solve the problem:

To rotate the linked list, we need to change the next pointer of kth node to NULL, the next pointer of the last node should point to the previous head node, and finally, change the head to (k+1)th node. So we need to get hold of three nodes: kth node, (k+1)th node, and last node
Traverse the list from the beginning and stop at kth node. store k’s next in a tem pointer and point k’s next to NULL then start traversing from tem and keep traversing till the end and point end node’s next to start node and make tem as the new head.

Follow the below steps to implement the idea:

• Initialize a count variable with 0 and pointer kthnode pointing to Null and current pointing to head node.
• Move from current till k-1 and point kthnode to current’s next and current’t next to NULL.
• Move current from kth node to end node and point current’s next to head. Below image shows how to rotate function works in the code : Below is the implementation of the above approach:

## C++

 `// C++ program to rotate` `// a linked list counter clock wise`   `#include ` `using` `namespace` `std;`   `/* Link list node */` `class` `Node {` `public``:` `    ``int` `data;` `    ``Node* next;` `};`   `// This function rotates a linked list` `// counter-clockwise and updates the` `// head. The function assumes that k is` `// smaller than size of linked list.` `// It doesn't modify the list if` `// k is greater than or equal to size` `void` `rotate(Node** head_ref, ``int` `k)` `{` `    ``if` `(k == 0)` `        ``return``;`   `    ``// Let us understand the below` `    ``// code for example k = 4 and` `    ``// list = 10->20->30->40->50->60.` `    ``Node* current = *head_ref;`   `    ``// current will either point to` `    ``// kth or NULL after this loop.` `    ``// current will point to node` `    ``// 40 in the above example` `    ``int` `count = 1;` `    ``while` `(count < k && current != NULL) {` `        ``current = current->next;` `        ``count++;` `    ``}`   `    ``// If current is NULL, k is greater than` `    ``// or equal to count of nodes in linked list.` `    ``// Don't change the list in this case` `    ``if` `(current == NULL)` `        ``return``;`   `    ``// current points to kth node.` `    ``// Store it in a variable. kthNode` `    ``// points to node 40 in the above example` `    ``Node* kthNode = current;`   `    ``// current will point to` `    ``// last node after this loop` `    ``// current will point to` `    ``// node 60 in the above example` `    ``while` `(current->next != NULL)` `        ``current = current->next;`   `    ``// Change next of last node to previous head` `    ``// Next of 60 is now changed to node 10` `    ``current->next = *head_ref;`   `    ``// Change head to (k+1)th node` `    ``// head is now changed to node 50` `    ``*head_ref = kthNode->next;`   `    ``// change next of kth node to NULL` `    ``// next of 40 is now NULL` `    ``kthNode->next = NULL;` `}`   `/* UTILITY FUNCTIONS */` `/* Function to push a node */` `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 linked list */` `void` `printList(Node* node)` `{` `    ``while` `(node != NULL) {` `        ``cout << node->data << ``" "``;` `        ``node = node->next;` `    ``}` `}`   `/* Driver code*/` `int` `main(``void``)` `{` `    ``/* Start with the empty list */` `    ``Node* head = NULL;`   `    ``// create a list 10->20->30->40->50->60` `    ``for` `(``int` `i = 60; i > 0; i -= 10)` `        ``push(&head, i);`   `    ``cout << ``"Given linked list \n"``;` `    ``printList(head);` `    ``rotate(&head, 4);`   `    ``cout << ``"\nRotated Linked list \n"``;` `    ``printList(head);`   `    ``return` `(0);` `}`   `// This code is contributed by rathbhupendra`

## C

 `// C program to rotate a linked list counter clock wise`   `#include ` `#include `   `/* Link list node */` `struct` `Node {` `    ``int` `data;` `    ``struct` `Node* next;` `};`   `// This function rotates a linked list counter-clockwise and` `// updates the head. The function assumes that k is smaller` `// than size of linked list. It doesn't modify the list if` `// k is greater than or equal to size` `void` `rotate(``struct` `Node** head_ref, ``int` `k)` `{` `    ``if` `(k == 0)` `        ``return``;`   `    ``// Let us understand the below code for example k = 4` `    ``// and list = 10->20->30->40->50->60.` `    ``struct` `Node* current = *head_ref;`   `    ``// current will either point to kth or NULL after this` `    ``// loop. current will point to node 40 in the above` `    ``// example` `    ``int` `count = 1;` `    ``while` `(count < k && current != NULL) {` `        ``current = current->next;` `        ``count++;` `    ``}`   `    ``// If current is NULL, k is greater than or equal to` `    ``// count of nodes in linked list. Don't change the list` `    ``// in this case` `    ``if` `(current == NULL)` `        ``return``;`   `    ``// current points to kth node. Store it in a variable.` `    ``// kthNode points to node 40 in the above example` `    ``struct` `Node* kthNode = current;`   `    ``// current will point to last node after this loop` `    ``// current will point to node 60 in the above example` `    ``while` `(current->next != NULL)` `        ``current = current->next;`   `    ``// Change next of last node to previous head` `    ``// Next of 60 is now changed to node 10` `    ``current->next = *head_ref;`   `    ``// Change head to (k+1)th node` `    ``// head is now changed to node 50` `    ``*head_ref = kthNode->next;`   `    ``// change next of kth node to NULL` `    ``// next of 40 is now NULL` `    ``kthNode->next = NULL;` `}`   `/* UTILITY FUNCTIONS */` `/* Function to push a node */` `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 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(``void``)` `{` `    ``/* Start with the empty list */` `    ``struct` `Node* head = NULL;`   `    ``// create a list 10->20->30->40->50->60` `    ``for` `(``int` `i = 60; i > 0; i -= 10)` `        ``push(&head, i);`   `    ``printf``(``"Given linked list \n"``);` `    ``printList(head);` `    ``rotate(&head, 4);`   `    ``printf``(``"\nRotated Linked list \n"``);` `    ``printList(head);`   `    ``return` `(0);` `}`

## Java

 `// Java program to rotate a linked list`   `class` `LinkedList {` `    ``Node head; ``// head of list`   `    ``/* Linked list Node*/` `    ``class` `Node {` `        ``int` `data;` `        ``Node next;` `        ``Node(``int` `d)` `        ``{` `            ``data = d;` `            ``next = ``null``;` `        ``}` `    ``}`   `    ``// This function rotates a linked list counter-clockwise` `    ``// and updates the head. The function assumes that k is` `    ``// smaller than size of linked list. It doesn't modify` `    ``// the list if k is greater than or equal to size` `    ``void` `rotate(``int` `k)` `    ``{` `        ``if` `(k == ``0``)` `            ``return``;`   `        ``// Let us understand the below code for example k =` `        ``// 4 and list = 10->20->30->40->50->60.` `        ``Node current = head;`   `        ``// current will either point to kth or NULL after` `        ``// this loop. current will point to node 40 in the` `        ``// above example` `        ``int` `count = ``1``;` `        ``while` `(count < k && current != ``null``) {` `            ``current = current.next;` `            ``count++;` `        ``}`   `        ``// If current is NULL, k is greater than or equal to` `        ``// count of nodes in linked list. Don't change the` `        ``// list in this case` `        ``if` `(current == ``null``)` `            ``return``;`   `        ``// current points to kth node. Store it in a` `        ``// variable. kthNode points to node 40 in the above` `        ``// example` `        ``Node kthNode = current;`   `        ``// current will point to last node after this loop` `        ``// current will point to node 60 in the above` `        ``// example` `        ``while` `(current.next != ``null``)` `            ``current = current.next;`   `        ``// Change next of last node to previous head` `        ``// Next of 60 is now changed to node 10`   `        ``current.next = head;`   `        ``// Change head to (k+1)th node` `        ``// head is now changed to node 50` `        ``head = kthNode.next;`   `        ``// change next of kth node to null` `        ``kthNode.next = ``null``;` `    ``}`   `    ``/*  Given a reference (pointer to pointer) to the head` `        ``of a list and an int, push a new node on the front` `        ``of the list. */` `    ``void` `push(``int` `new_data)` `    ``{` `        ``/* 1 & 2: Allocate the Node &` `                  ``Put in the data*/` `        ``Node new_node = ``new` `Node(new_data);`   `        ``/* 3. Make next of new Node as head */` `        ``new_node.next = head;`   `        ``/* 4. Move the head to point to new Node */` `        ``head = new_node;` `    ``}`   `    ``void` `printList()` `    ``{` `        ``Node temp = head;` `        ``while` `(temp != ``null``) {` `            ``System.out.print(temp.data + ``" "``);` `            ``temp = temp.next;` `        ``}` `        ``System.out.println();` `    ``}`   `    ``/* Driver program to test above functions */` `    ``public` `static` `void` `main(String args[])` `    ``{` `        ``LinkedList llist = ``new` `LinkedList();`   `        ``// create a list 10->20->30->40->50->60` `        ``for` `(``int` `i = ``60``; i >= ``10``; i -= ``10``)` `            ``llist.push(i);`   `        ``System.out.println(``"Given list"``);` `        ``llist.printList();`   `        ``llist.rotate(``4``);`   `        ``System.out.println(``"Rotated Linked List"``);` `        ``llist.printList();` `    ``}` `} ``/* This code is contributed by Rajat Mishra */`

## Python

 `# Python program to rotate a linked list`   `# Node class`     `class` `Node:`   `    ``# Constructor to initialize the node object` `    ``def` `__init__(``self``, data):` `        ``self``.data ``=` `data` `        ``self``.``next` `=` `None`     `class` `LinkedList:`   `    ``# Function to initialize head` `    ``def` `__init__(``self``):` `        ``self``.head ``=` `None`   `    ``# Function to insert a new node at the beginning` `    ``def` `push(``self``, new_data):` `        ``# allocate node and put the data` `        ``new_node ``=` `Node(new_data)`   `        ``# Make next of new node as head` `        ``new_node.``next` `=` `self``.head`   `        ``# move the head to point to the new Node` `        ``self``.head ``=` `new_node`   `    ``# Utility function to print it the linked LinkedList` `    ``def` `printList(``self``):` `        ``temp ``=` `self``.head` `        ``while``(temp):` `            ``print` `temp.data,` `            ``temp ``=` `temp.``next`   `    ``# This function rotates a linked list counter-clockwise and` `    ``# updates the head. The function assumes that k is smaller` `    ``# than size of linked list. It doesn't modify the list if` `    ``# k is greater than of equal to size` `    ``def` `rotate(``self``, k):` `        ``if` `k ``=``=` `0``:` `            ``return`   `        ``# Let us understand the below code for example k = 4` `        ``# and list = 10->20->30->40->50->60` `        ``current ``=` `self``.head`   `        ``# current will either point to kth or NULL after` `        ``# this loop` `        ``# current will point to node 40 in the above example` `        ``count ``=` `1` `        ``while``(count < k ``and` `current ``is` `not` `None``):` `            ``current ``=` `current.``next` `            ``count ``+``=` `1`   `        ``# If current is None, k is greater than or equal` `        ``# to count of nodes in linked list. Don't change` `        ``# the list in this case` `        ``if` `current ``is` `None``:` `            ``return`   `        ``# current points to kth node. Store it in a variable` `        ``# kth node points to node 40 in the above example` `        ``kthNode ``=` `current`   `        ``# current will point to last node after this loop` `        ``# current will point to node 60 in above example` `        ``while``(current.``next` `is` `not` `None``):` `            ``current ``=` `current.``next`   `        ``# Change next of last node to previous head` `        ``# Next of 60 is now changed to node 10` `        ``current.``next` `=` `self``.head`   `        ``# Change head to (k + 1)th node` `        ``# head is not changed to node 50` `        ``self``.head ``=` `kthNode.``next`   `        ``# change next of kth node to NULL` `        ``# next of 40 is not NULL` `        ``kthNode.``next` `=` `None`     `# Driver program to test above function` `llist ``=` `LinkedList()`   `# Create a list 10->20->30->40->50->60` `for` `i ``in` `range``(``60``, ``0``, ``-``10``):` `    ``llist.push(i)`   `print` `"Given linked list"` `llist.printList()` `llist.rotate(``4``)`   `print` `"\nRotated Linked list"` `llist.printList()`   `# This code is contributed by Nikhil Kumar Singh(nickzuck_007)`

## C#

 `// C# program to rotate a linked list` `using` `System;`   `public` `class` `LinkedList {` `    ``Node head; ``// head of list`   `    ``/* Linked list Node*/` `    ``public` `class` `Node {` `        ``public` `int` `data;` `        ``public` `Node next;` `        ``public` `Node(``int` `d)` `        ``{` `            ``data = d;` `            ``next = ``null``;` `        ``}` `    ``}`   `    ``// This function rotates a linked list` `    ``// counter-clockwise and updates the head.` `    ``// The function assumes that k is smaller` `    ``// than size of linked list. It doesn't modify` `    ``// the list if k is greater than or equal to size` `    ``void` `rotate(``int` `k)` `    ``{` `        ``if` `(k == 0)` `            ``return``;`   `        ``// Let us understand the below` `        ``// code for example k = 4` `        ``// and list = 10->20->30->40->50->60.` `        ``Node current = head;`   `        ``// current will either point to kth` `        ``// or NULL after this loop. current` `        ``// will point to node 40 in the above example` `        ``int` `count = 1;` `        ``while` `(count < k && current != ``null``) {` `            ``current = current.next;` `            ``count++;` `        ``}`   `        ``// If current is NULL, k is greater than` `        ``// or equal to count of nodes in linked list.` `        ``// Don't change the list in this case` `        ``if` `(current == ``null``)` `            ``return``;`   `        ``// current points to kth node.` `        ``// Store it in a variable.` `        ``// kthNode points to node` `        ``// 40 in the above example` `        ``Node kthNode = current;`   `        ``// current will point to` `        ``// last node after this loop` `        ``// current will point to` `        ``// node 60 in the above example` `        ``while` `(current.next != ``null``)` `            ``current = current.next;`   `        ``// Change next of last node to previous head` `        ``// Next of 60 is now changed to node 10`   `        ``current.next = head;`   `        ``// Change head to (k+1)th node` `        ``// head is now changed to node 50` `        ``head = kthNode.next;`   `        ``// change next of kth node to null` `        ``kthNode.next = ``null``;` `    ``}`   `    ``/* Given a reference (pointer to pointer) to the head` `        ``of a list and an int, push a new node on the front` `        ``of the list. */` `    ``void` `push(``int` `new_data)` `    ``{` `        ``/* 1 & 2: Allocate the Node &` `                ``Put in the data*/` `        ``Node new_node = ``new` `Node(new_data);`   `        ``/* 3. Make next of new Node as head */` `        ``new_node.next = head;`   `        ``/* 4. Move the head to point to new Node */` `        ``head = new_node;` `    ``}`   `    ``void` `printList()` `    ``{` `        ``Node temp = head;` `        ``while` `(temp != ``null``) {` `            ``Console.Write(temp.data + ``" "``);` `            ``temp = temp.next;` `        ``}` `        ``Console.WriteLine();` `    ``}`   `    ``/* Driver code */` `    ``public` `static` `void` `Main()` `    ``{` `        ``LinkedList llist = ``new` `LinkedList();`   `        ``// create a list 10->20->30->40->50->60` `        ``for` `(``int` `i = 60; i >= 10; i -= 10)` `            ``llist.push(i);`   `        ``Console.WriteLine(``"Given list"``);` `        ``llist.printList();`   `        ``llist.rotate(4);`   `        ``Console.WriteLine(``"Rotated Linked List"``);` `        ``llist.printList();` `    ``}` `}`   `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``

Output

```Given linked list
10 20 30 40 50 60