Move last element to front of a given Linked List | Set 2

Last Updated : 18 Dec, 2023

Given a singly linked list and an integer K. The task is to append last K elements of the linked list to front. Examples:

Input: 1 -> 2 -> 3 -> 4 -> 5 -> 6, k = 3
Output : 4 -> 5 -> 6 -> 1 -> 2 -> 3
Input: 1 -> 2 -> 3 -> 4 -> 5 -> 6, k = 7
Output : 6 -> 1 -> 2 -> 3 -> 4 -> 5

Prerequisites: Move last element to front of a given Linked List Approach:

Loop over (k % n) times, Where n is the number of elements of the linked list.
Each time, delete one node from the end of the linked list.
Simultaneously insert that deleted node at the beginning of the linked list.

Below is the implementation of the above approach :

C++

// CPP Program to move k last elements 
// to front in a given linked list 
#include<iostream>
using namespace std;
  
// A linked list node 
class Node
{
    public:
      
    int data;
    Node* next;
    Node(int d) {
        data = d;
        next = NULL;
    }
};
  
// Function to add a new node at the
// end/tail of Linked List 
void insertAtTail(Node*& head, Node*& tail, int d ) {
    Node* newnode = new Node(d);
    if(tail == NULL) {
        tail = head = newnode;
        return;
    }
  
    tail->next = newnode;
    tail = newnode;
}
  
// Function to add a node at the
// beginning of Linked List 
void insertAtHead(Node*& head, Node*& tail, 
                           Node*& deletedNode) 
{
    if(head == NULL) {
        head = tail = deletedNode;
        return;
    }
    deletedNode->next = head;
    head = deletedNode;
    return;
}
  
// Function to add a node at the beginning of Linked List 
Node* deleteAtTail(Node*& head, Node*& tail) {
    Node* deleted = tail;
    Node* temp = head;
  
    while(temp->next->next != NULL) {
        temp = temp->next;
    }
  
    temp->next = NULL;
    tail = temp;
    return deleted;
}
  
// k can be more than n, so this function takes the modulus 
// of k with n and delete nodes from end k 
// times and simultaneously insert it in front
void appendAtFront(Node*& head, Node*& tail, int n, int k) 
{
    k = k % n;
    while(k != 0) {
        Node* deleted = deleteAtTail(head, tail);
        insertAtHead(head, tail, deleted);
        k--;
    }
}
  
// Function to print nodes in a given linked list 
void printLinkedList(Node* head) {
    while(head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
    cout << endl;
}
  
// Driver Code 
int main() 
{
    // Pointer to the start of the linked list
    Node* head = NULL;
      
    // Pointer to the end of the linked list
    Node* tail = NULL; 
      
    // Number of elements in the linked list
    int n = 6; 
      
    // Building linked list
    insertAtTail(head, tail, 1);
    insertAtTail(head, tail, 2);
    insertAtTail(head, tail, 3);
    insertAtTail(head, tail, 4);
    insertAtTail(head, tail, 5);
    insertAtTail(head, tail, 6);
      
      
    // Printing linked list before 
    // appending the linked list
    cout << "Linked List before appending: ";
    printLinkedList(head);
      
    // Number of elements to be appended
    int k = 7;
      
    // Function call
    appendAtFront(head, tail, n, k); 
      
    // Printing linked list after appending the list
    cout << "Linked List after appending "<<k<<" elements: ";
    printLinkedList(head); 
}

Java

// JAVA Program to move k last elements 
// to front in a given linked list 

import java.io.*;

class Node {
    int data;
    Node next;
    Node(int data)
    {
        this.data = data;
        this.next = null;
    }
}

class LinkedList {
    Node head;
    Node tail;

    // Function to add a new node at the end/tail of Linked
    // List
    public void insertAtTail(int data)
    {
        Node newnode = new Node(data);
        if (tail == null) {
            tail = head = newnode;
            return;
        }
        tail.next = newnode;
        tail = newnode;
    }

    // Function to add a node at the beginning of Linked
    // List
    public void insertAtHead(Node deletedNode)
    {
        if (head == null) {
            head = tail = deletedNode;
            return;
        }
        deletedNode.next = head;
        head = deletedNode;
    }

    // Function to delete a node at the end of Linked List
    public Node deleteAtTail()
    {
        Node deleted = tail;
        Node temp = head;
        while (temp.next.next != null) {
            temp = temp.next;
        }
        temp.next = null;
        tail = temp;
        return deleted;
    }

    // k can be more than n, so this function takes the
    // modulus of k with n and delete nodes from end k times
    // and simultaneously insert it in front
    public void appendAtFront(int n, int k)
    {
        k = k % n;
        while (k != 0) {
            Node deleted = deleteAtTail();
            insertAtHead(deleted);
            k--;
        }
    }

    // Function to print nodes in a given linked list
    public void printLinkedList()
    {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
        System.out.println();
    }
}

class GFG {
    public static void main(String[] args)
    {
        LinkedList ll = new LinkedList();
        ll.insertAtTail(1);
        ll.insertAtTail(2);
        ll.insertAtTail(3);
        ll.insertAtTail(4);
        ll.insertAtTail(5);
        ll.insertAtTail(6);

        System.out.print("Linked List before appending: ");
        ll.printLinkedList();

        int k = 7;

        ll.appendAtFront(6, k);

        System.out.print("Linked List after appending " + k
                         + " elements: ");
        ll.printLinkedList();
    }
}

// This code is contributed by lokesh.

Python3

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None


class LinkedList:
    def __init__(self):
        self.head = None
        self.tail = None

    # Function to add a new node at the end/tail of Linked List
    def insert_at_tail(self, data):
        new_node = Node(data)
        if self.tail is None:
            self.tail = self.head = new_node
            return
        self.tail.next = new_node
        self.tail = new_node

    # Function to add a node at the beginning of Linked List
    def insert_at_head(self, deleted_node):
        if self.head is None:
            self.head = self.tail = deleted_node
            return
        deleted_node.next = self.head
        self.head = deleted_node

    # Function to delete a node at the end of Linked List
    def delete_at_tail(self):
        deleted = self.tail
        temp = self.head
        while temp.next.next is not None:
            temp = temp.next
        temp.next = None
        self.tail = temp
        return deleted

    # k can be more than n, so this function takes the modulus
    # of k with n and deletes nodes from the end k times while
    # simultaneously inserting them at the front
    def append_at_front(self, n, k):
        k = k % n
        while k != 0:
            deleted = self.delete_at_tail()
            self.insert_at_head(deleted)
            k -= 1

    # Function to print nodes in a given linked list
    def print_linked_list(self):
        temp = self.head
        while temp is not None:
            print(temp.data, end=" ")
            temp = temp.next
        print()


# Driver Code
if __name__ == "__main__":
    ll = LinkedList()
    ll.insert_at_tail(1)
    ll.insert_at_tail(2)
    ll.insert_at_tail(3)
    ll.insert_at_tail(4)
    ll.insert_at_tail(5)
    ll.insert_at_tail(6)

    print("Linked List before appending: ", end="")
    ll.print_linked_list()

    k = 7

    ll.append_at_front(6, k)

    print("Linked List after appending", k, "elements: ", end="")
    ll.print_linked_list()

using System;

class Node {
    public int data;
    public Node next;

    public Node(int data)
    {
        this.data = data;
        this.next = null;
    }
}

class LinkedList {
    public Node head;
    public Node tail;

    // Function to add a new node at the end/tail of Linked
    // List
    public void InsertAtTail(int data)
    {
        Node newNode = new Node(data);
        if (tail == null) {
            tail = head = newNode;
            return;
        }
        tail.next = newNode;
        tail = newNode;
    }

    // Function to add a node at the beginning of Linked
    // List
    public void InsertAtHead(Node deletedNode)
    {
        if (head == null) {
            head = tail = deletedNode;
            return;
        }
        deletedNode.next = head;
        head = deletedNode;
    }

    // Function to delete a node at the end of Linked List
    public Node DeleteAtTail()
    {
        Node deleted = tail;
        Node temp = head;
        while (temp.next.next != null) {
            temp = temp.next;
        }
        temp.next = null;
        tail = temp;
        return deleted;
    }

    // k can be more than n, so this function takes the
    // modulus of k with n and deletes nodes from the end k
    // times while simultaneously inserting them at the
    // front
    public void AppendAtFront(int n, int k)
    {
        k = k % n;
        while (k != 0) {
            Node deleted = DeleteAtTail();
            InsertAtHead(deleted);
            k--;
        }
    }

    // Function to print nodes in a given linked list
    public void PrintLinkedList()
    {
        Node temp = head;
        while (temp != null) {
            Console.Write(temp.data + " ");
            temp = temp.next;
        }
        Console.WriteLine();
    }
}

class Program {
    public static void Main()
    {
        LinkedList ll = new LinkedList();
        ll.InsertAtTail(1);
        ll.InsertAtTail(2);
        ll.InsertAtTail(3);
        ll.InsertAtTail(4);
        ll.InsertAtTail(5);
        ll.InsertAtTail(6);

        Console.Write("Linked List before appending: ");
        ll.PrintLinkedList();

        int k = 7;

        ll.AppendAtFront(6, k);

        Console.Write("Linked List after appending " + k
                      + " elements: ");
        ll.PrintLinkedList();
    }
}

JavaScript

class Node {
    constructor(data) {
        this.data = data;
        this.next = null;
    }
}

class LinkedList {
    constructor() {
        this.head = null;
        this.tail = null;
    }

    // Function to add a new node at the end/tail of Linked List
    insertAtTail(data) {
        const newNode = new Node(data);
        if (this.tail === null) {
            this.tail = this.head = newNode;
            return;
        }
        this.tail.next = newNode;
        this.tail = newNode;
    }

    // Function to add a node at the beginning of Linked List
    insertAtHead(deletedNode) {
        if (this.head === null) {
            this.head = this.tail = deletedNode;
            return;
        }
        deletedNode.next = this.head;
        this.head = deletedNode;
    }

    // Function to delete a node at the end of Linked List
    deleteAtTail() {
        if (this.head === null) {
            return null; // Empty list, nothing to delete
        }

        const deleted = this.tail;
        let temp = this.head;

        // If there is only one element in the list
        if (temp === this.tail) {
            this.head = this.tail = null;
            return deleted;
        }

        while (temp.next.next !== null) {
            temp = temp.next;
        }

        temp.next = null;
        this.tail = temp;
        return deleted;
    }

    // k can be more than n, so this function takes the
    // modulus of k with n and delete nodes from end k times
    // and simultaneously insert it in front
    appendAtFront(n, k) {
        k = k % n;
        while (k !== 0) {
            const deleted = this.deleteAtTail();
            this.insertAtHead(deleted);
            k--;
        }
    }

    // Function to print nodes in a given linked list
    printLinkedList() {
        let temp = this.head;
        while (temp !== null) {
            process.stdout.write(temp.data + " ");
            temp = temp.next;
        }
        console.log();
    }
}

// Driver Code
const ll = new LinkedList();
ll.insertAtTail(1);
ll.insertAtTail(2);
ll.insertAtTail(3);
ll.insertAtTail(4);
ll.insertAtTail(5);
ll.insertAtTail(6);

process.stdout.write("Linked List before appending: ");
ll.printLinkedList();

const k = 7;

ll.appendAtFront(6, k);

process.stdout.write("Linked List after appending " + k + " elements: ");
ll.printLinkedList();

Output

Linked List before appending: 1 2 3 4 5 6 
Linked List after appending 7 elements: 6 1 2 3 4 5

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

Move the Kth element to the Front of a Doubly Linked List

balindam

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Move last element to front of a given Linked List | Set 2

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