# Move all occurrences of an element to end in a linked list

• Difficulty Level : Medium
• Last Updated : 08 Jul, 2022

Given a linked list and a key in it, the task is to move all occurrences of the given key to the end of the linked list, keeping the order of all other elements the same.

Examples:

```Input  : 1 -> 2 -> 2 -> 4 -> 3
key = 2
Output : 1 -> 4 -> 3 -> 2 -> 2

Input  : 6 -> 6 -> 7 -> 6 -> 3 -> 10
key = 6
Output : 7 -> 3 -> 10 -> 6 -> 6 -> 6```

A simple solution is to one by one find all occurrences of a given key in the linked list. For every found occurrence, insert it at the end. We do it till all occurrences of the given key are moved to the end.

Time Complexity: O(n2), as we will be using nested loops to find the node with the key and insert it at the end of the linked list.
Auxiliary Space: O(1), as we are not using any extra space.

Efficient Solution 1: is to keep two pointers:

pCrawl => Pointer to traverse the whole list one by one.
pKey => Pointer to an occurrence of the key if a key is found. Else the same as pCrawl.

We start both of the above pointers from the head of the linked list. We move pKey only when pKey is not pointing to a key. We always move pCrawl. So, when pCrawl and pKey are not the same, we must have found a key that lies before pCrawl, so we swap between pCrawl and pKey, and move pKey to the next location. The loop invariant is, after swapping of data, all elements from pKey to pCrawl are keys.

Below is the implementation of this approach.

## C++

 `// C++ program to move all occurrences of a``// given key to end.``#include ` `// A Linked list Node``struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};` `// A utility function to create a new node.``struct` `Node* newNode(``int` `x)``{``    ``Node* temp = ``new` `Node;``    ``temp->data = x;``    ``temp->next = NULL;``}` `// Utility function to print the elements``// in Linked list``void` `printList(Node* head)``{``    ``struct` `Node* temp = head;``    ``while` `(temp != NULL) {``        ``printf``(``"%d "``, temp->data);``        ``temp = temp->next;``    ``}``    ``printf``(``"\n"``);``}` `// Moves all occurrences of given key to``// end of linked list.``void` `moveToEnd(Node* head, ``int` `key)``{``    ``// Keeps track of locations where key``    ``// is present.``    ``struct` `Node* pKey = head;` `    ``// Traverse list``    ``struct` `Node* pCrawl = head;``    ``while` `(pCrawl != NULL) {``        ``// If current pointer is not same as pointer``        ``// to a key location, then we must have found``        ``// a key in linked list. We swap data of pCrawl``        ``// and pKey and move pKey to next position.``        ``if` `(pCrawl != pKey && pCrawl->data != key) {``            ``pKey->data = pCrawl->data;``            ``pCrawl->data = key;``            ``pKey = pKey->next;``        ``}` `        ``// Find next position where key is present``        ``if` `(pKey->data != key)``            ``pKey = pKey->next;` `        ``// Moving to next Node``        ``pCrawl = pCrawl->next;``    ``}``}` `// Driver code``int` `main()``{``    ``Node* head = newNode(10);``    ``head->next = newNode(20);``    ``head->next->next = newNode(10);``    ``head->next->next->next = newNode(30);``    ``head->next->next->next->next = newNode(40);``    ``head->next->next->next->next->next = newNode(10);``    ``head->next->next->next->next->next->next = newNode(60);` `    ``printf``(``"Before moveToEnd(), the Linked list is\n"``);``    ``printList(head);` `    ``int` `key = 10;``    ``moveToEnd(head, key);` `    ``printf``(``"\nAfter moveToEnd(), the Linked list is\n"``);``    ``printList(head);` `    ``return` `0;``}`

## Java

 `// Java program to move all occurrences of a``// given key to end.``class` `GFG {` `    ``// A Linked list Node``    ``static` `class` `Node {``        ``int` `data;``        ``Node next;``    ``}` `    ``// A utility function to create a new node.``    ``static` `Node newNode(``int` `x)``    ``{``        ``Node temp = ``new` `Node();``        ``temp.data = x;``        ``temp.next = ``null``;``        ``return` `temp;``    ``}` `    ``// Utility function to print the elements``    ``// in Linked list``    ``static` `void` `printList(Node head)``    ``{``        ``Node temp = head;``        ``while` `(temp != ``null``) {``            ``System.out.printf(``"%d "``, temp.data);``            ``temp = temp.next;``        ``}``        ``System.out.printf(``"\n"``);``    ``}` `    ``// Moves all occurrences of given key to``    ``// end of linked list.``    ``static` `void` `moveToEnd(Node head, ``int` `key)``    ``{``        ``// Keeps track of locations where key``        ``// is present.``        ``Node pKey = head;` `        ``// Traverse list``        ``Node pCrawl = head;``        ``while` `(pCrawl != ``null``) {``            ``// If current pointer is not same as pointer``            ``// to a key location, then we must have found``            ``// a key in linked list. We swap data of pCrawl``            ``// and pKey and move pKey to next position.``            ``if` `(pCrawl != pKey && pCrawl.data != key) {``                ``pKey.data = pCrawl.data;``                ``pCrawl.data = key;``                ``pKey = pKey.next;``            ``}` `            ``// Find next position where key is present``            ``if` `(pKey.data != key)``                ``pKey = pKey.next;` `            ``// Moving to next Node``            ``pCrawl = pCrawl.next;``        ``}``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String args[])``    ``{``        ``Node head = newNode(``10``);``        ``head.next = newNode(``20``);``        ``head.next.next = newNode(``10``);``        ``head.next.next.next = newNode(``30``);``        ``head.next.next.next.next = newNode(``40``);``        ``head.next.next.next.next.next = newNode(``10``);``        ``head.next.next.next.next.next.next = newNode(``60``);` `        ``System.out.printf(``"Before moveToEnd(), the Linked list is\n"``);``        ``printList(head);` `        ``int` `key = ``10``;``        ``moveToEnd(head, key);` `        ``System.out.printf(``"\nAfter moveToEnd(), the Linked list is\n"``);``        ``printList(head);``    ``}``}` `// This code is contributed by Arnab Kundu`

## Python3

 `# Python3 program to move all occurrences of a``# given key to end.` `# Linked List node``class` `Node:``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data``        ``self``.``next` `=` `None` `# A utility function to create a new node.``def` `newNode(x):` `    ``temp ``=` `Node(``0``)``    ``temp.data ``=` `x``    ``temp.``next` `=` `None``    ``return` `temp` `# Utility function to print the elements``# in Linked list``def` `printList( head):` `    ``temp ``=` `head``    ``while` `(temp !``=` `None``) :``        ``print``( temp.data,end ``=` `" "``)``        ``temp ``=` `temp.``next``    ` `    ``print``()` `# Moves all occurrences of given key to``# end of linked list.``def` `moveToEnd(head, key):` `    ``# Keeps track of locations where key``    ``# is present.``    ``pKey ``=` `head` `    ``# Traverse list``    ``pCrawl ``=` `head``    ``while` `(pCrawl !``=` `None``) :``        ` `        ``# If current pointer is not same as pointer``        ``# to a key location, then we must have found``        ``# a key in linked list. We swap data of pCrawl``        ``# and pKey and move pKey to next position.``        ``if` `(pCrawl !``=` `pKey ``and` `pCrawl.data !``=` `key) :``            ``pKey.data ``=` `pCrawl.data``            ``pCrawl.data ``=` `key``            ``pKey ``=` `pKey.``next``        ` `        ``# Find next position where key is present``        ``if` `(pKey.data !``=` `key):``            ``pKey ``=` `pKey.``next` `        ``# Moving to next Node``        ``pCrawl ``=` `pCrawl.``next``    ` `    ``return` `head` `# Driver code``head ``=` `newNode(``10``)``head.``next` `=` `newNode(``20``)``head.``next``.``next` `=` `newNode(``10``)``head.``next``.``next``.``next` `=` `newNode(``30``)``head.``next``.``next``.``next``.``next` `=` `newNode(``40``)``head.``next``.``next``.``next``.``next``.``next` `=` `newNode(``10``)``head.``next``.``next``.``next``.``next``.``next``.``next` `=` `newNode(``60``)` `print``(``"Before moveToEnd(), the Linked list is\n"``)``printList(head)` `key ``=` `10``head ``=` `moveToEnd(head, key)` `print``(``"\nAfter moveToEnd(), the Linked list is\n"``)``printList(head)` `# This code is contributed by Arnab Kundu`

## C#

 `// C# program to move all occurrences of a``// given key to end.``using` `System;` `class` `GFG {` `    ``// A Linked list Node``    ``public` `class` `Node {``        ``public` `int` `data;``        ``public` `Node next;``    ``}` `    ``// A utility function to create a new node.``    ``static` `Node newNode(``int` `x)``    ``{``        ``Node temp = ``new` `Node();``        ``temp.data = x;``        ``temp.next = ``null``;``        ``return` `temp;``    ``}` `    ``// Utility function to print the elements``    ``// in Linked list``    ``static` `void` `printList(Node head)``    ``{``        ``Node temp = head;``        ``while` `(temp != ``null``) {``            ``Console.Write(``"{0} "``, temp.data);``            ``temp = temp.next;``        ``}``        ``Console.Write(``"\n"``);``    ``}` `    ``// Moves all occurrences of given key to``    ``// end of linked list.``    ``static` `void` `moveToEnd(Node head, ``int` `key)``    ``{``        ``// Keeps track of locations where key``        ``// is present.``        ``Node pKey = head;` `        ``// Traverse list``        ``Node pCrawl = head;``        ``while` `(pCrawl != ``null``) {``            ``// If current pointer is not same as pointer``            ``// to a key location, then we must have found``            ``// a key in linked list. We swap data of pCrawl``            ``// and pKey and move pKey to next position.``            ``if` `(pCrawl != pKey && pCrawl.data != key) {``                ``pKey.data = pCrawl.data;``                ``pCrawl.data = key;``                ``pKey = pKey.next;``            ``}` `            ``// Find next position where key is present``            ``if` `(pKey.data != key)``                ``pKey = pKey.next;` `            ``// Moving to next Node``            ``pCrawl = pCrawl.next;``        ``}``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``Node head = newNode(10);``        ``head.next = newNode(20);``        ``head.next.next = newNode(10);``        ``head.next.next.next = newNode(30);``        ``head.next.next.next.next = newNode(40);``        ``head.next.next.next.next.next = newNode(10);``        ``head.next.next.next.next.next.next = newNode(60);` `        ``Console.Write(``"Before moveToEnd(), the Linked list is\n"``);``        ``printList(head);` `        ``int` `key = 10;``        ``moveToEnd(head, key);` `        ``Console.Write(``"\nAfter moveToEnd(), the Linked list is\n"``);``        ``printList(head);``    ``}``}` `// This code has been contributed by 29AjayKumar`

## Javascript

 ``

Output

```Before moveToEnd(), the Linked list is
10 20 10 30 40 10 60

After moveToEnd(), the Linked list is
20 30 40 60 10 10 10
```

Time Complexity: O(n), as we are using a loop to traverse n times. Where n is the number of nodes in the linked list.
Auxiliary Space: O(1), as we are not using any extra space.

Efficient Solution 2 :

1. Traverse the linked list and take a pointer at the tail.
2. Now, check for the key and node->data. If they are equal, move the node to last-next, else move ahead.

## C++

 `// C++ code to remove key element to end of linked list``#include``using` `namespace` `std;` `// A Linked list Node``struct` `Node``{``    ``int` `data;``    ``struct` `Node* next;``};` `// A utility function to create a new node.``struct` `Node* newNode(``int` `x)``{``    ``Node* temp = ``new` `Node;``    ``temp->data = x;``    ``temp->next = NULL;``}` `// Function to remove key to end``Node *keyToEnd(Node* head, ``int` `key)``{` `    ``// Node to keep pointing to tail``    ``Node* tail = head;``    ``if` `(head == NULL)``    ``{``        ``return` `NULL;``    ``}``    ``while` `(tail->next != NULL)``    ``{``        ``tail = tail->next;``    ``}``    ` `    ``// Node to point to last of linked list``    ``Node* last = tail;``    ``Node* current = head;``    ``Node* prev = NULL;``    ` `    ``// Node prev2 to point to previous when head.data!=key``    ``Node* prev2 = NULL;``    ` `    ``// loop to perform operations to remove key to end``    ``while` `(current != tail)``    ``{``        ``if` `(current->data == key && prev2 == NULL)``        ``{``            ``prev = current;``            ``current = current->next;``            ``head = current;``            ``last->next = prev;``            ``last = last->next;``            ``last->next = NULL;``            ``prev = NULL;``        ``}``        ``else``        ``{``            ``if` `(current->data == key && prev2 != NULL)``            ``{``                ``prev = current;``                ``current = current->next;``                ``prev2->next = current;``                ``last->next = prev;``                ``last = last->next;``                ``last->next = NULL;``            ``}``            ``else` `if` `(current != tail)``            ``{``                ``prev2 = current;``                ``current = current->next;``            ``}``        ``}``    ``}``    ``return` `head;``}` `// Function to display linked list``void` `printList(Node* head)``{``    ``struct` `Node* temp = head;``    ``while` `(temp != NULL)``    ``{``        ``printf``(``"%d "``, temp->data);``        ``temp = temp->next;``    ``}``    ``printf``(``"\n"``);``}`  `// Driver Code``int` `main()``{``    ``Node* root = newNode(5);``    ``root->next = newNode(2);``    ``root->next->next = newNode(2);``    ``root->next->next->next = newNode(7);``    ``root->next->next->next->next = newNode(2);``    ``root->next->next->next->next->next = newNode(2);``    ``root->next->next->next->next->next->next = newNode(2);` `    ``int` `key = 2;``    ``cout << ``"Linked List before operations :"``;``    ``printList(root);``    ``cout << ``"\nLinked List after operations :"``;``    ``root = keyToEnd(root, key);``    ``printList(root);``    ``return` `0;``}` `// This code is contributed by Rajout-Ji`

## Java

 `// Java code to remove key element to end of linked list``import` `java.util.*;` `// Node class``class` `Node {``    ``int` `data;``    ``Node next;` `    ``public` `Node(``int` `data)``    ``{``        ``this``.data = data;``        ``this``.next = ``null``;``    ``}``}` `class` `gfg {` `    ``static` `Node root;` `    ``// Function to remove key to end``    ``public` `static` `Node keyToEnd(Node head, ``int` `key)``    ``{` `        ``// Node to keep pointing to tail``        ``Node tail = head;` `        ``if` `(head == ``null``) {``            ``return` `null``;``        ``}` `        ``while` `(tail.next != ``null``) {``            ``tail = tail.next;``        ``}` `        ``// Node to point to last of linked list``        ``Node last = tail;` `        ``Node current = head;``        ``Node prev = ``null``;` `        ``// Node prev2 to point to previous when head.data!=key``        ``Node prev2 = ``null``;` `        ``// loop to perform operations to remove key to end``        ``while` `(current != tail) {``            ``if` `(current.data == key && prev2 == ``null``) {``                ``prev = current;``                ``current = current.next;``                ``head = current;``                ``last.next = prev;``                ``last = last.next;``                ``last.next = ``null``;``                ``prev = ``null``;``            ``}``            ``else` `{``                ``if` `(current.data == key && prev2 != ``null``) {``                    ``prev = current;``                    ``current = current.next;``                    ``prev2.next = current;``                    ``last.next = prev;``                    ``last = last.next;``                    ``last.next = ``null``;``                ``}``                ``else` `if` `(current != tail) {``                    ``prev2 = current;``                    ``current = current.next;``                ``}``            ``}``        ``}``        ``return` `head;``    ``}` `    ``// Function to display linked list``    ``public` `static` `void` `display(Node root)``    ``{``        ``while` `(root != ``null``) {``            ``System.out.print(root.data + ``" "``);``            ``root = root.next;``        ``}``    ``}` `    ``// Driver Code``    ``public` `static` `void` `main(String args[])``    ``{``        ``root = ``new` `Node(``5``);``        ``root.next = ``new` `Node(``2``);``        ``root.next.next = ``new` `Node(``2``);``        ``root.next.next.next = ``new` `Node(``7``);``        ``root.next.next.next.next = ``new` `Node(``2``);``        ``root.next.next.next.next.next = ``new` `Node(``2``);``        ``root.next.next.next.next.next.next = ``new` `Node(``2``);` `        ``int` `key = ``2``;``        ``System.out.println(``"Linked List before operations :"``);``        ``display(root);``        ``System.out.println(``"\nLinked List after operations :"``);``        ``root = keyToEnd(root, key);``        ``display(root);``    ``}``}`

## Python3

 `# Python3 code to remove key element to``# end of linked list`` ` `# A Linked list Node``class` `Node:``    ` `    ``def` `__init__(``self``, data):``        ` `        ``self``.data ``=` `data``        ``self``.``next` `=` `None``        ` `# A utility function to create a new node.``def` `newNode(x):``    ` `    ``temp ``=` `Node(x)``    ``return` `temp` `# Function to remove key to end``def` `keyToEnd(head, key):` `    ``# Node to keep pointing to tail``    ``tail ``=` `head``    ` `    ``if` `(head ``=``=` `None``):``        ``return` `None``    ` `    ``while` `(tail.``next` `!``=` `None``):``        ``tail ``=` `tail.``next``    ` `    ``# Node to point to last of linked list``    ``last ``=` `tail``    ``current ``=` `head``    ``prev ``=` `None``     ` `    ``# Node prev2 to point to previous``    ``# when head.data!=key``    ``prev2 ``=` `None``     ` `    ``# Loop to perform operations to``    ``# remove key to end``    ``while` `(current !``=` `tail):``        ``if` `(current.data ``=``=` `key ``and` `prev2 ``=``=` `None``):``            ``prev ``=` `current``            ``current ``=` `current.``next``            ``head ``=` `current``            ``last.``next` `=` `prev``            ``last ``=` `last.``next``            ``last.``next` `=` `None``            ``prev ``=` `None` `        ``else``:``            ``if` `(current.data ``=``=` `key ``and` `prev2 !``=` `None``):``                ``prev ``=` `current``                ``current ``=` `current.``next``                ``prev2.``next` `=` `current``                ``last.``next` `=` `prev``                ``last ``=` `last.``next``                ``last.``next` `=` `None``            ` `            ``else` `if` `(current !``=` `tail):``                ``prev2 ``=` `current``                ``current ``=` `current.``next``                ` `    ``return` `head` `# Function to display linked list``def` `printList(head):` `    ``temp ``=` `head``    ` `    ``while` `(temp !``=` `None``):``        ``print``(temp.data, end ``=` `' '``)``        ``temp ``=` `temp.``next``    ` `    ``print``()``    ` `# Driver Code``if` `__name__``=``=``'__main__'``:``    ` `    ``root ``=` `newNode(``5``)``    ``root.``next` `=` `newNode(``2``)``    ``root.``next``.``next` `=` `newNode(``2``)``    ``root.``next``.``next``.``next` `=` `newNode(``7``)``    ``root.``next``.``next``.``next``.``next` `=` `newNode(``2``)``    ``root.``next``.``next``.``next``.``next``.``next` `=` `newNode(``2``)``    ``root.``next``.``next``.``next``.``next``.``next``.``next` `=` `newNode(``2``)`` ` `    ``key ``=` `2``    ``print``(``"Linked List before operations :"``)``    ``printList(root)``    ``print``(``"Linked List after operations :"``)``    ``root ``=` `keyToEnd(root, key)``    ` `    ``printList(root)``    ` `# This code is contributed by rutvik_56`

## C#

 `// C# code to remove key``// element to end of linked list``using` `System;` `// Node class``public` `class` `Node {``    ``public` `int` `data;``    ``public` `Node next;` `    ``public` `Node(``int` `data)``    ``{``        ``this``.data = data;``        ``this``.next = ``null``;``    ``}``}` `class` `GFG {` `    ``static` `Node root;` `    ``// Function to remove key to end``    ``public` `static` `Node keyToEnd(Node head, ``int` `key)``    ``{` `        ``// Node to keep pointing to tail``        ``Node tail = head;` `        ``if` `(head == ``null``) {``            ``return` `null``;``        ``}` `        ``while` `(tail.next != ``null``) {``            ``tail = tail.next;``        ``}` `        ``// Node to point to last of linked list``        ``Node last = tail;` `        ``Node current = head;``        ``Node prev = ``null``;` `        ``// Node prev2 to point to``        ``// previous when head.data!=key``        ``Node prev2 = ``null``;` `        ``// loop to perform operations``        ``// to remove key to end``        ``while` `(current != tail) {``            ``if` `(current.data == key && prev2 == ``null``) {``                ``prev = current;``                ``current = current.next;``                ``head = current;``                ``last.next = prev;``                ``last = last.next;``                ``last.next = ``null``;``                ``prev = ``null``;``            ``}``            ``else` `{``                ``if` `(current.data == key && prev2 != ``null``) {``                    ``prev = current;``                    ``current = current.next;``                    ``prev2.next = current;``                    ``last.next = prev;``                    ``last = last.next;``                    ``last.next = ``null``;``                ``}``                ``else` `if` `(current != tail) {``                    ``prev2 = current;``                    ``current = current.next;``                ``}``            ``}``        ``}``        ``return` `head;``    ``}` `    ``// Function to display linked list``    ``public` `static` `void` `display(Node root)``    ``{``        ``while` `(root != ``null``) {``            ``Console.Write(root.data + ``" "``);``            ``root = root.next;``        ``}``    ``}` `    ``// Driver Code``    ``public` `static` `void` `Main()``    ``{``        ``root = ``new` `Node(5);``        ``root.next = ``new` `Node(2);``        ``root.next.next = ``new` `Node(2);``        ``root.next.next.next = ``new` `Node(7);``        ``root.next.next.next.next = ``new` `Node(2);``        ``root.next.next.next.next.next = ``new` `Node(2);``        ``root.next.next.next.next.next.next = ``new` `Node(2);` `        ``int` `key = 2;``        ``Console.WriteLine(``"Linked List before operations :"``);``        ``display(root);``        ``Console.WriteLine(``"\nLinked List after operations :"``);``        ``root = keyToEnd(root, key);``        ``display(root);``    ``}``}` `// This code is contributed by PrinciRaj1992`

## Javascript

 ``

Output

```Linked List before operations :5 2 2 7 2 2 2

Linked List after operations :5 7 2 2 2 2 2
```

Time Complexity: O(n), as we are using a loop to traverse n times. Where n is the number of nodes in the linked list.
Auxiliary Space: O(1), as we are not using any extra space.

Thanks to Ravinder Kumar for suggesting this method.

Efficient Solution 3: is to maintain a separate list of keys. We initialize this list of keys as empty. We traverse the given list. For every key found, we remove it from the original list and insert it into a separate list of keys. We finally link the list of keys at the end of the remaining given list.

Time Complexity: O(n), as we are using a loop to traverse n times. Where n is the number of nodes in the linked list.
Auxiliary Space: O(1), as we are not using any extra space.

This article is contributed by MAZHAR IMAM KHAN. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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