Swap Kth node from beginning with Kth node from end in a Doubly Linked List

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Prerequisites: Doubly Linked List
Given a doubly-linked list, the task is to swap K^th node from the beginning with K^th node from the ending.
Note: Please note here the nodes are swapped and not the data in the nodes.

Examples:

Input: DLL = 1 <-> 2 <-> 3 <-> 4 <-> 5 <-> 6, K = 3
Output: 1 2 4 3 5 6
Explanation:
Third node from the beginning(3) is swapped with third node from the ending(4).

Input: DLL = 1 <-> 2 <-> 3 <-> 4 <-> 5, K = 1
Output: 5 2 3 4 1

Approach: The idea is to traverse to the K^th element from the beginning and K^th node from the ending and change the previous and next pointers. Let K1 be the K^th node from beginning and K2 be K^th node from ending. Then:

The previous node to K2 has to be changed to the previous node of K1.
The next node to K2 has to be changed to the next node of K1.
The previous node to K1 has to be changed to the previous node of K2.
The next node to K1 has to be changed to the next node of K2.

Below is the implementation of the above approach:

C++

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
 
// Node structure of the doubly linked list
struct Node {
    int data;
    Node* next;
    Node* previous;
};
 
// Class of the doubly linked list
class GFG {
    // head of the doubly linked list
    Node* head;
 
    // tail of the doubly linked list
    Node* tail;
 
    public:
 
    // Default constructor
    GFG()
    {
        head = tail = NULL;
    }
 
    // Function to return the head of the
    // doubly linked list
    Node* getHead()
    {
        return head;
    }
 
    // Function to set the head of the
    // doubly linked list
    void setHead(Node* head)
    {
        this->head = head;
    }
 
    // Function to return the tail of the
    // doubly linked list
    Node* getTail()
    {
        return tail;
    }
 
    // Function to set the tail of the
    // doubly linked list
    void setTail(Node* tail)
    {
        this->tail = tail;
    }
 
    // Function to replace Kth node from
    // beginning with Kth node from end
    void swapNode(Node* headReference,
                  Node* tailReference, int k)
    {
 
        // If K is 1, then the first node
        // has to be swapped with the
        // last node in the doubly linked list
        if (k == 1) {
            swapFirstAndLast(headReference,
                             tailReference);
            return;
        }
 
        // If k is N, then the last node
        // has to be swapped with the
        // first node in the doubly linked list
        int nodeCount = getCount(headReference);
        if (k == nodeCount) {
            swapFirstAndLast(headReference,
                             tailReference);
            return;
        }
 
        // If the K<sup>th</sup> node from
        // the beginning and K<sup>th</sup> node
        // from the ending are same
        if (2 * k - 1 == nodeCount) {
            return;
        }
 
        // fNode represents K<sup>th</sup> node
        // from the beginning
        Node* fNode = headReference;
        for (int i = 1; i < k; i++) {
            fNode = fNode->next;
        }
        Node* fNodePrevious = fNode->previous;
        Node* fNodeNext = fNode->next;
 
        // sNode represents K<sup>th</sup> node
        // from the ending
        Node* sNode = tailReference;
        for (int i = 1; i < k; i++) {
            sNode = sNode->previous;
        }
 
        Node* sNodePrevious = sNode->previous;
        Node* sNodeNext = sNode->next;
 
        // Checking if any of the pointers is null
        // and interchanging the pointers
        if (fNodePrevious != NULL && sNode != NULL) {
 
            fNodePrevious->next = sNode;
            sNode->previous
                = fNodePrevious;
            sNode->next = fNodeNext;
            fNodeNext->previous
                = sNode;
        }
        if (sNodePrevious != NULL
            && sNodeNext != NULL) {
 
            sNodeNext->previous
                = fNode;
            fNode->next
                = sNodeNext;
            sNodePrevious
                ->next = fNode;
            fNode->previous
                = sNodePrevious;
        }
    }
 
    // Function to swap the first and
    // last node in the doubly linked list
    void swapFirstAndLast(Node* headReference,
                          Node* tailReference)
    {
        Node* headRef = headReference;
        Node* tailRef = tailReference;
 
        headReference
            = headReference->next;
        tailReference
            = tailReference->previous;
 
        tailReference->next
            = headRef;
        headRef->previous
            = tailReference;
        headRef->next = NULL;
        this->setTail(tailReference
                         ->next);
 
        headReference->previous
            = tailRef;
        tailRef->next
            = headReference;
        tailRef->previous
            = NULL;
        this->setHead(headReference
                         ->previous);
    }
 
    // Function to return the number of nodes
    // in the linked list
    int getCount(Node* headReference)
    {
        int nodeCount = 0;
        while (headReference != NULL) {
            nodeCount++;
            headReference
                = headReference->next;
        }
        return nodeCount;
    }
 
    // Function to print the Linked List
    void printList(Node* headReference)
    {
        if (headReference == NULL) {
            cout << "Doubly linked list is empty";
            return;
        }
        else {
            while (headReference
                   != NULL) {
                cout << headReference->data
                     << " ";
                headReference
                    = headReference->next;
            }
        }
    }
 
    // Function to insert a node at
    // the end of the doubly linked list
    void push(int data)
    {
        Node* newNode = new Node;
        newNode->data = data;
        newNode->next = NULL;
        newNode->previous = NULL;
 
        if (head == NULL) {
            head = tail = newNode;
        }
        else {
            tail->next = newNode;
            newNode->previous = tail;
            tail = newNode;
        }
    }
};
 
// Driver code
int main()
{
 
    // Creating an object for the class
    GFG list;
 
    // Adding data to the linked list
    list.push(1);
    list.push(2);
    list.push(3);
    list.push(4);
    list.push(5);
 
    // Calling the function
    int K = 2;
    list.swapNode(list.getHead(),
                  list.getTail(), K);
    list.printList(list.getHead());
 
    return 0;
}

Java

// Java implementation of the approach
 
public class GFG {
 
    // Doubly Linked List implementation
    private class Node {
        private int data;
        private Node next;
        private Node previous;
 
        public Node(int data, Node next,
                    Node previous)
        {
            this.data = data;
            this.next = next;
            this.previous = previous;
        }
 
        public int getData()
        {
            return data;
        }
 
        public void setData(int data)
        {
            this.data = data;
        }
 
        public Node getNext()
        {
            return next;
        }
 
        public void setNext(Node next)
        {
            this.next = next;
        }
 
        public Node getPrevious()
        {
            return previous;
        }
 
        public void setPrevious(Node previous)
        {
            this.previous = previous;
        }
    }
 
    private Node head;
    private Node tail;
 
    public GFG()
    {
        this.head = null;
        this.tail = null;
    }
 
    public Node getHead()
    {
        return head;
    }
 
    public void setHead(Node head)
    {
        this.head = head;
    }
 
    public Node getTail()
    {
        return tail;
    }
 
    public void setTail(Node tail)
    {
        this.tail = tail;
    }
 
    // Function to replace Kth node from
    // beginning with Kth node from end
    public void swapNode(Node headReference,
                         Node tailReference, int k)
    {
 
        // If K is 1, then the first node
        // has to be swapped with the
        // last node in the doubly linked list
        if (k == 1) {
            swapFirstAndLast(headReference,
                             tailReference);
            return;
        }
 
        // If k is N, then the last node
        // has to be swapped with the
        // first node in the doubly linked list
        int nodeCount = getCount(headReference);
        if (k == nodeCount) {
            swapFirstAndLast(headReference,
                             tailReference);
            return;
        }
 
        // If the K<sup>th</sup> node from
        // the beginning and K<sup>th</sup> node
        // from the ending are same
        if (2 * k - 1 == nodeCount) {
            return;
        }
 
        // fNode represents K<sup>th</sup> node
        // from the beginning
        Node fNode = headReference;
        for (int i = 1; i < k; i++) {
            fNode = fNode.getNext();
        }
        Node fNodePrevious = fNode.getPrevious();
        Node fNodeNext = fNode.getNext();
 
        // sNode represents K<sup>th</sup> node
        // from the ending
        Node sNode = tailReference;
        for (int i = 1; i < k; i++) {
            sNode = sNode.getPrevious();
        }
 
        Node sNodePrevious = sNode.getPrevious();
        Node sNodeNext = sNode.getNext();
 
        // Checking if any of the pointers is null
        // and interchanging the pointers
        if (fNodePrevious != null && sNode != null) {
 
            fNodePrevious.setNext(sNode);
            sNode.setPrevious(fNodePrevious);
            sNode.setNext(fNodeNext);
            fNodeNext.setPrevious(sNode);
        }
        if (sNodePrevious != null && sNodeNext != null) {
 
            sNodeNext.setPrevious(fNode);
            fNode.setNext(sNodeNext);
            sNodePrevious.setNext(fNode);
            fNode.setPrevious(sNodePrevious);
        }
    }
 
    // Function to swap the first and
    // last node in the doubly linked list
    private void swapFirstAndLast(
        Node headReference,
        Node tailReference)
    {
        Node headRef = headReference;
        Node tailRef = tailReference;
 
        headReference
            = headReference.getNext();
        tailReference
            = tailReference.getPrevious();
 
        tailReference.setNext(headRef);
        headRef.setPrevious(tailReference);
        headRef.setNext(null);
        this.setTail(tailReference.getNext());
 
        headReference.setPrevious(tailRef);
        tailRef.setNext(headReference);
        tailRef.setPrevious(null);
        this.setHead(headReference
                         .getPrevious());
    }
 
    // Function to return the number of nodes
    // in the linked list
    private int getCount(Node headReference)
    {
        int nodeCount = 0;
        while (headReference != null) {
            nodeCount++;
            headReference = headReference
                                .getNext();
        }
        return nodeCount;
    }
 
    // Function to print the Linked List
    public void printList(Node headReference)
    {
        if (headReference == null) {
            System.out.println(
                "Doubly linked list is empty");
            return;
        }
        else {
            while (headReference != null) {
                System.out.print(
                    headReference.getData()
                    + " ");
                headReference
                    = headReference.getNext();
            }
        }
    }
 
    // Function to insert a node at
    // the end of the doubly linked list
    public void push(int data)
    {
        Node newNode
            = new Node(data, null, null);
 
        if (head == null) {
            head = tail = newNode;
        }
        else {
            tail.setNext(newNode);
            newNode.setPrevious(tail);
            tail = newNode;
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
 
        // Creating an object for the class
        GFG list = new GFG();
 
        // Adding data to the linked list
        list.push(1);
        list.push(2);
        list.push(3);
        list.push(4);
        list.push(5);
 
        // Calling the function
        int K = 2;
        list.swapNode(list.getHead(),
                      list.getTail(), K);
        list.printList(list.getHead());
    }
}

Python3

# Python implementation of the approach
 
# Node structure of the doubly linked list
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
        self.previous = None
 
    def getData(self):
        return self.data
 
    def setData(self, data):
        self.data = data
 
    def getNext(self, ):
        return next
 
    def setNext(self, next):
        self.next = next
 
    def getPrevious(self):
        return previous
 
    def setPrevious(self, previous):
        self.previous = previous
 
# Class of the doubly linked list
class GFG:
    # head of the doubly linked list
    def __init__(self):
        self.head = None
        # tail of the doubly linked list
        self.tail = None
 
    # Function to return the head of the doubly linked list
    def getHead(self):
        return self.head
 
    # Function to set the head of the doubly linked list
    def setHead(self, head):
        self.head = head
 
    # Function to return the tail of the doubly linked list
    def getTail(self):
        return self.tail
 
    # Function to set the tail of the doubly linked list
    def setTail(self, tail):
        self.tail = tail
 
    # Function to replace Kth node from beginning with Kth node from end
    def swapNode(self, headReference, tailReference, k):
 
        # If K is 1, then the first node has to be swapped with the last node in the doubly linked list
        if k == 1:
            self.swapFirstAndLast(headReference, tailReference)
            return
 
        # If k is N, then the last node has to be swapped with the first node in the doubly linked list
        nodeCount = self.getCount(headReference)
        if k == nodeCount:
            self.swapFirstAndLast(headReference, tailReference)
            return
 
        # If the Kth node from the beginning and Kth node from the ending are same
        if 2 * k - 1 == nodeCount:
            return
 
        # fNode represents Kth node from the beginning
        fNode = headReference
        for i in range(1, k):
            fNode = fNode.next
        fNodePrevious = fNode.previous
        fNodeNext = fNode.next
 
        # sNode represents Kth node from the ending
        sNode = tailReference
        for i in range(1, k):
            sNode = sNode.previous
 
        sNodePrevious = sNode.previous
        sNodeNext = sNode.next
 
        # Checking if any of the pointers is null and interchanging the pointers
        if fNodePrevious != None and sNode != None:
            fNodePrevious.next = sNode
            sNode.previous = fNodePrevious
            sNode.next = fNodeNext
            fNodeNext.previous = sNode
        if sNodePrevious != None and sNodeNext != None:
            sNodeNext.previous = fNode
            fNode.next = sNodeNext
            sNodePrevious.next = fNode
            fNode.previous = sNodePrevious
 
    # Function to swap the first and last node in the doubly linked list
    def swapFirstAndLast(self, headReference, tailReference):
        headRef = headReference
        tailRef = tailReference
 
        headReference = headReference.next
        tailReference = tailReference.previous
 
        tailReference.next = headRef
        headRef.previous = tailReference
        headRef.next = None
        self.setTail(tailReference.next)
 
        headReference.previous = tailRef
        tailRef.next = headReference
        tailRef.previous = None
        self.setHead(headReference.previous)
 
    # Function to return the number of nodes in the linked list
    def getCount(self, headReference):
        nodeCount = 0
        while headReference != None:
            nodeCount += 1
            headReference = headReference.next
        return nodeCount
     
    # Function to insert a node at
    # the end of the doubly linked list
    def push(self, data):
        newNode = Node(data)
        if (self.head == None):
            self.head = self.tail = newNode
        else:
            self.tail.setNext(newNode)
            newNode.setPrevious(self.tail)
            self.tail = newNode
     
    def printList(self, headReference):
        if headReference == None: 
            print("Doubly linked list is empty")
            return
        while headReference:
            print(headReference.data,end = ' ')
            headReference = headReference.next
        print()
     
# Driver code
# Creating an object for the class
list = GFG()
 
# Adding data to the linked list
list.push(1)
list.push(2)
list.push(3)
list.push(4)
list.push(5)
 
# Calling the function
K = 2
list.swapNode(list.getHead(),list.getTail(), K)
list.printList(list.getHead())

C#

// C# implementation of the approach
using System;
public class GFG {
  
    // Doubly Linked List implementation
    private class Node {
        private int data;
        private Node next;
        private Node previous;
  
        public Node(int data, Node next,
                    Node previous)
        {
            this.data = data;
            this.next = next;
            this.previous = previous;
        }
  
        public int getData()
        {
            return data;
        }
  
        public void setData(int data)
        {
            this.data = data;
        }
  
        public Node getNext()
        {
            return next;
        }
  
        public void setNext(Node next)
        {
            this.next = next;
        }
  
        public Node getPrevious()
        {
            return previous;
        }
  
        public void setPrevious(Node previous)
        {
            this.previous = previous;
        }
    }
  
    private Node head;
    private Node tail;
  
    public GFG()
    {
        this.head = null;
        this.tail = null;
    }
  
    Node getHead()
    {
        return head;
    }
  
    void setHead(Node head)
    {
        this.head = head;
    }
  
    Node getTail()
    {
        return tail;
    }
  
    void setTail(Node tail)
    {
        this.tail = tail;
    }
  
    // Function to replace Kth node from
    // beginning with Kth node from end
    void swapNode(Node headReference,
                         Node tailReference, int k)
    {
  
        // If K is 1, then the first node
        // has to be swapped with the
        // last node in the doubly linked list
        if (k == 1) {
            swapFirstAndLast(headReference,
                             tailReference);
            return;
        }
  
        // If k is N, then the last node
        // has to be swapped with the
        // first node in the doubly linked list
        int nodeCount = getCount(headReference);
        if (k == nodeCount) {
            swapFirstAndLast(headReference,
                             tailReference);
            return;
        }
  
        // If the K<sup>th</sup> node from
        // the beginning and K<sup>th</sup> node
        // from the ending are same
        if (2 * k - 1 == nodeCount) {
            return;
        }
  
        // fNode represents K<sup>th</sup> node
        // from the beginning
        Node fNode = headReference;
        for (int i = 1; i < k; i++) {
            fNode = fNode.getNext();
        }
        Node fNodePrevious = fNode.getPrevious();
        Node fNodeNext = fNode.getNext();
  
        // sNode represents K<sup>th</sup> node
        // from the ending
        Node sNode = tailReference;
        for (int i = 1; i < k; i++) {
            sNode = sNode.getPrevious();
        }
  
        Node sNodePrevious = sNode.getPrevious();
        Node sNodeNext = sNode.getNext();
  
        // Checking if any of the pointers is null
        // and interchanging the pointers
        if (fNodePrevious != null && sNode != null) {
  
            fNodePrevious.setNext(sNode);
            sNode.setPrevious(fNodePrevious);
            sNode.setNext(fNodeNext);
            fNodeNext.setPrevious(sNode);
        }
        if (sNodePrevious != null && sNodeNext != null) {
  
            sNodeNext.setPrevious(fNode);
            fNode.setNext(sNodeNext);
            sNodePrevious.setNext(fNode);
            fNode.setPrevious(sNodePrevious);
        }
    }
  
    // Function to swap the first and
    // last node in the doubly linked list
    private void swapFirstAndLast(
        Node headReference,
        Node tailReference)
    {
        Node headRef = headReference;
        Node tailRef = tailReference;
  
        headReference
            = headReference.getNext();
        tailReference
            = tailReference.getPrevious();
  
        tailReference.setNext(headRef);
        headRef.setPrevious(tailReference);
        headRef.setNext(null);
        this.setTail(tailReference.getNext());
  
        headReference.setPrevious(tailRef);
        tailRef.setNext(headReference);
        tailRef.setPrevious(null);
        this.setHead(headReference
                         .getPrevious());
    }
  
    // Function to return the number of nodes
    // in the linked list
    private int getCount(Node headReference)
    {
        int nodeCount = 0;
        while (headReference != null) {
            nodeCount++;
            headReference = headReference
                                .getNext();
        }
        return nodeCount;
    }
  
    // Function to print the Linked List
    void printList(Node headReference)
    {
        if (headReference == null) {
            Console.WriteLine(
                "Doubly linked list is empty");
            return;
        }
        else {
            while (headReference != null) {
                Console.Write(
                    headReference.getData()
                    + " ");
                headReference
                    = headReference.getNext();
            }
        }
    }
  
    // Function to insert a node at
    // the end of the doubly linked list
    void Push(int data)
    {
        Node newNode
            = new Node(data, null, null);
  
        if (head == null) {
            head = tail = newNode;
        }
        else {
            tail.setNext(newNode);
            newNode.setPrevious(tail);
            tail = newNode;
        }
    }
  
    // Driver code
    public static void Main(String[] args)
    {
  
        // Creating an object for the class
        GFG list = new GFG();
  
        // Adding data to the linked list
        list.Push(1);
        list.Push(2);
        list.Push(3);
        list.Push(4);
        list.Push(5);      
             
        // Calling the function
        int K = 2;
        list.swapNode(list.getHead(),
                      list.getTail(), K);
        list.printList(list.getHead());
    }
}
 
// This code is contributed by 29AjayKumar

Output

1 4 3 2 5

Time Complexity: O(K), As we are traversing till Kth element from tail and head of the list and then changing the links which is a O(1) operation.
Auxiliary Space: O(1), As constant extra space is used.

Method 2: Without swapping the elements and without using temporary node.

Approach: There are 3 cases in order to swap the nodes.

Swapping the first and the last nodes (k = 1)
Swapping the ordinary Kth node from the beginning and Kth node from the end.
Swapping middle nodes

Case 1: Swap first and last nodes (k = 1)

Steps:

Make the list as a circular linked list
Change the previous pointer of the first node to the last but one node (20 in example figure)
Change the next pointer of last but one node to the last node. In this case it will be 60.
After swapping, make the head as the first node.

   Consider p and q are the nodes which are to be swapped,
   
   head = q; //change head pointer to point to head node
   last = p; //change last pointer to point to last node

swapping first and last nodes

Case 2: Swapping the ordinary Kth node from the beginning and Kth node from the end.

Steps:

Let us consider K = 2. So the nodes to be swapped or interchanged are 20 and 50 as show in the figure.
Make both the first and next pointers of the nodes which are to be swapped to point to the previous nodes. To do this, we need to change the links of the previous nodes to point to the node which is after the node to be swapped.

    Consider the nodes to be swapped are p and q:
    
    //Change the link of the next pointer of the previous node to point to
    //the next node of to be swapped node.
    q.first.next = q.next;    
    p.first.next = p.next; // Same procedure for the other node
    
    //Make sure to change the previous/first pointer of the next node to 
    //point to the previous of to be swapped node.
    q.next.first = q.first;     
    p.next.first = p.first;
    
    //Both the first and next pointers points to the previous node as shown in the below figure.
    q.next = q.first;
    p.next = p.first;

3. Interchange the pointers of one node to be swapped nodes with the other to be swapped node. (step 3 denotes the figure after interchanging).

4. Make the required changes in the links in order to make it as a complete list.

General case

Case 3: Swapping the middle nodes

Steps:

This case is same as the case 2 and the only change is, the nodes which are to be swapped are middle nodes. So both of them are together (side-by-side).
Consider p is the first node to be swapped and q is the second node to be swapped.
Point the next pointer of previous node of p to the next node of q. This step is done to omit p and q nodes.
In the same way, point the first pointer of next node of q to the previous node of q.
Change the links of p and q so that both the nodes points to the previous node of p (step2 in the below figure).
Make the links of p and q accordingly to make the nodes swap their positions.

To swap middle nodes

Implementation:

C++

// CPP program to swap Kth node from beginning with
// the Kth node from the end without using temporary
// node and without swapping the data
#include <bits/stdc++.h>
using namespace std;
 
// class Node
class Node {
public:
    int data;
    Node *first, *next;
    Node(int data)
    {
        this->data = data;
        first = NULL;
        next = NULL;
    }
};
 
// function for inserting new node at the
// end of the list using last pointer
void AddLast(int data, Node*& head, Node*& last)
{
    Node* temp = new Node(data);
    if (!head) {
        head = temp;
        last = temp;
    }
    else {
        last->next = temp;
        temp->first = last;
        last = temp;
    }
}
 
// function for printing the doubly linked list
void printList(Node* head)
{
    Node* p = head;
    while (p) {
        cout << p->data << "<->";
        p = p->next;
    }
    cout << "NULL" << endl;
}
 
// function for swapping Kth node from
// beginning with Kth node from the end
void swapKthNodes(Node*& head, Node*& last, int k)
{
    int count = 1;
    Node *p = head, *q = last;
    // case 1: to swap the start and end nodes
    // case 1 figure
    if (k == 1) {
        q->first->next = p;
        p->first = q->first;
 
        q->next = p->next;
        p->next->first = q;
 
        // change these links to NULL to the break circular
        // link
        p->next = NULL;
        q->first = NULL;
 
        head = q;
        last = p;
    }
    else {
        while (p != NULL && q != NULL && count < k) {
            count++;
            p = p->next;
            q = q->first;
        }
 
        // case 3: if the nodes to be swapped are the middle
        // nodes given in the figure
        if (p->next == q) {
            p->first->next = p->next->next;
            q->next->first = p->first;
 
            p->next = p->first;
            q->first = q->next = p->first;
 
            q->next = p;
            p->next->next->first = p;
            p->next = p->first->next;
 
            p->first->next = q;
            p->first = q;
        }
        // case 2: other than middle nodes
        // given in case 2 figure
        else {
            q->first->next = q->next;
            q->next->first = q->first;
            q->next = q->first;
 
            p->first->next = p->next;
            p->next->first = p->first;
            p->next = p->first;
 
            p->first = q->first;
            q->first = p->next;
 
            p->next = p->first;
            q->next = q->first;
 
            q->next = q->next->next;
            q->first->next = q;
            q->next->first = q;
 
            p->next = p->next->next;
            p->first->next = p;
            p->next->first = p;
        }
    }
}
 
// Driver function
int main()
{
    // head pointer for pointing to start of the linked list
    // last pointer for pointing to last node of the linked
    // list
    Node *head = NULL, *last = NULL;
 
    // function calls for inserting
    // at the end of the list
    AddLast(10, head, last);
    AddLast(20, head, last);
    AddLast(30, head, last);
    AddLast(40, head, last);
    AddLast(50, head, last);
    AddLast(60, head, last);
 
    cout << "Before swapping:" << endl;
    // print list before swapping the nodes
    printList(head);
    cout << endl;
 
    // function call for swapping Kth nodes
    swapKthNodes(head, last, 1);
 
    cout << "After swapping nodes for k = 1:" << endl;
    // print list after swapping the nodes
    printList(head);
    cout << endl;
 
    swapKthNodes(head, last, 2);
    cout << "After swapping nodes for k = 2:" << endl;
    printList(head);
    cout << endl;
 
    swapKthNodes(head, last, 3);
    cout << "After swapping nodes for k = 3 (middle):"
         << endl;
    printList(head);
    cout << endl;
    return 0;
}
 
// This code is contributed Tapesh(tapeshdua420)

Java

// Java program to swap Kth node from beginning with
// the Kth node from the end without using temporary
// node and without swapping the data
public class GFG
{
 
  // head pointer for pointing to start of the linked list
  // last pointer for pointing to last node of the linked list
  Node head = null,last = null;
 
  // class Node
  class Node{
    int data;
    Node first,next;
    Node(int data){
      this.data = data;
      first = null;
      next = null;
    }
  }
 
  // function for inserting new node at the
  // end of the list using last pointer
  void AddLast(int data) {
    Node temp = new Node(data);
    if(head == null) {
      head = temp;
      last = temp;
    }
    else {
      last.next = temp;
      temp.first = last;
      last = temp;
    }
  }
 
  // function for printing the doubly linked list
  void printList() {
    Node p = head;
    while(p!=null) {
      System.out.print(p.data+"<->");
      p = p.next;
    }
    System.out.print("null");
    System.out.println();
  }
 
  // function for swapping Kth node from 
  // beginning with Kth node from the end
  void swapKthNodes(int k) {
    int count = 1;
    Node p = head, q = last;
 
    // case 1: to swap the start and end nodes
    // case 1 figure
    if(k == 1) {
      q.first.next = p;
      p.first = q.first;
 
      q.next = p.next;
      p.next.first = q;
 
      // change these links to null to the break circular link
      p.next = null;
      q.first = null;
 
      head = q;
      last = p;
    }
    else {
      while(p != null  &&  q != null  &&  count < k) {
        count++;
        p = p.next;
        q = q.first;
      }
 
      // case 3: if the nodes to be swapped are the middle nodes
      // given in the figure
      if(p.next == q) {
        p.first.next = p.next.next;
        q.next.first = p.first;
 
        p.next = p.first;
        q.first = q.next = p.first;
 
        q.next = p;
        p.next.next.first = p;
        p.next = p.first.next;
 
        p.first.next = q;
        p.first = q;
      }
      // case 2: other than middle nodes
      // given in case 2 figure
      else {
        q.first.next = q.next;
        q.next.first = q.first;
        q.next = q.first;
 
        p.first.next = p.next;
        p.next.first = p.first;
        p.next = p.first;
 
        p.first = q.first;
        q.first = p.next;
 
        p.next = p.first;
        q.next = q.first;
 
        q.next = q.next.next;
        q.first.next = q;
        q.next.first = q;
 
        p.next = p.next.next;
        p.first.next = p;
        p.next.first = p;
      }
    }
  }
 
  // Driver function
  public static void main(String args[])
  {
 
    // class object
    GFG list = new GFG();
 
    // function calls for inserting 
    // at the end of the list
    list.AddLast(10);
    list.AddLast(20);
    list.AddLast(30);
    list.AddLast(40);
    list.AddLast(50);
    list.AddLast(60);
 
    System.out.println("Before swapping:");
    // print list before swapping the nodes
    list.printList();
    System.out.println();
 
    // function call for swapping Kth nodes
    list.swapKthNodes(1);
 
    System.out.println("After swapping nodes for k = 1:");
 
    // print list after swapping the nodes
    list.printList();
    System.out.println();
 
    list.swapKthNodes(2);
    System.out.println("After swapping nodes for k = 2:");
    list.printList();
    System.out.println();
 
    list.swapKthNodes(3);
    System.out.println("After swapping nodes for k = 3 (middle):");
    list.printList();
    System.out.println();
  }
}
 
// This code is contributed by Likhita AVL

Python3

# Python program to swap Kth node from beginning with
# the Kth node from the end without using temporary
# node and without swapping the data
 
# class Node
class Node:
    def __init__(self, data):
        self.data = data
        self.first = None
        self.next = None
 
 
class GFG:
    # head pointer for pointing to start of the linked list
    # last pointer for pointing to last node of the linked list
    def __init__(self):
        self.head = None
        self.last = None
 
    # function for inserting new node at the
    # end of the list using last pointer
    def AddLast(self, data):
        temp = Node(data)
        if self.head == None:
            self.head = temp
            self.last = temp
        else:
            self.last.next = temp
            temp.first = self.last
            self.last = temp
 
    # function for printing the doubly linked list
    def printList(self):
        p = self.head
        while p != None:
            print(p.data, "<->", end="")
            p = p.next
        print("null")
 
    # function for swapping Kth node from
    # beginning with Kth node from the end
    def swapKthNodes(self, k):
        count = 1
        p = self.head
        q = self.last
 
        # case 1: to swap the start and end nodes
        # case 1 figure
        if k == 1:
            q.first.next = p
            p.first = q.first
 
            q.next = p.next
            p.next.first = q
 
            # change these links to null to the break circular link
            p.next = None
            q.first = None
 
            self.head = q
            self.last = p
 
        else:
            while p != None and q != None and count < k:
                count += 1
                p = p.next
                q = q.first
 
            # case 3: if the nodes to be swapped are the middle nodes
            # given in the figure
            if p.next == q:
                p.first.next = p.next.next
                q.next.first = p.first
 
                p.next = p.first
                q.first = q.next = p.first
 
                q.next = p
                p.next.next.first = p
                p.next = p.first.next
 
                p.first.next = q
                p.first = q
 
            # case 2: other than middle nodes
            # given in case 2 figure
            else:
                q.first.next = q.next
                q.next.first = q.first
                q.next = q.first
 
                p.first.next = p.next
                p.next.first = p.first
                p.next = p.first
 
                p.first = q.first
                q.first = p.next
 
                p.next = p.first
                q.next = q.first
 
                q.next = q.next.next
                q.first.next = q
                q.next.first = q
 
                p.next = p.next.next
                p.first.next = p
                p.next.first = p
 
 
# Driver function
if __name__ == '__main__':
    # class object
    list = GFG()
 
    # function calls for inserting
    # at the end of the list
    list.AddLast(10)
    list.AddLast(20)
    list.AddLast(30)
    list.AddLast(40)
    list.AddLast(50)
    list.AddLast(60)
 
    print("Before swapping:")
    # print list before swapping the nodes
    list.printList()
    print()
 
    # function call for swapping Kth nodes
    list.swapKthNodes(1)
 
    print("After swapping nodes for k = 1:")
    # print list after swapping the nodes
    list.printList()
    print()
 
    list.swapKthNodes(2)
    print("After swapping nodes for k = 2:")
    list.printList()
    print()
 
    list.swapKthNodes(3)
    print("After swapping nodes for k = 3 (middle):")
    list.printList()
    print()
 
# This code is contributed by Tapesh(tapeshuda420)

C#

// C# program to swap Kth node from beginning with the Kth
// node from the end without using temporary node and without
// swapping the data
using System;
 
public class GFG {
 
    // class Node
    class Node {
        public int data;
        public Node first, next;
        public Node(int data)
        {
            this.data = data;
            first = null;
            next = null;
        }
    }
 
    // head pointer for pointing to start of the linked list
    // last pointer for pointing to last node of the linked
    // list
    Node head = null, last = null;
 
    // function for inserting new node at the end of the
    // list using last pointer
    void AddLast(int data)
    {
        Node temp = new Node(data);
        if (head == null) {
            head = temp;
            last = temp;
        }
        else {
            last.next = temp;
            temp.first = last;
            last = temp;
        }
    }
 
    // function for printing the doubly linked list
    void printList()
    {
        Node p = head;
        while (p != null) {
            Console.Write(p.data + "<->");
            p = p.next;
        }
        Console.Write("null");
        Console.WriteLine();
    }
 
    // function for swapping Kth node from beginning with
    // Kth node from the end
    void swapKthNodes(int k)
    {
        int count = 1;
        Node p = head, q = last;
        // case 1: to swap the start and end nodes case 1
        // figure
        if (k == 1) {
            q.first.next = p;
            p.first = q.first;
 
            q.next = p.next;
            p.next.first = q;
 
            // change these links to null to the break
            // circular link
            p.next = null;
            q.first = null;
 
            head = q;
            last = p;
        }
        else {
            while (p != null && q != null && count < k) {
                count++;
                p = p.next;
                q = q.first;
            }
 
            // case 3: if the nodes to be swapped are the
            // middle nodes given in the figure
            if (p.next == q) {
                p.first.next = p.next.next;
                q.next.first = p.first;
 
                p.next = p.first;
                q.first = q.next = p.first;
 
                q.next = p;
                p.next.next.first = p;
                p.next = p.first.next;
 
                p.first.next = q;
                p.first = q;
            }
            // case 2: other than middle nodes given in case
            // 2 figure
            else {
                q.first.next = q.next;
                q.next.first = q.first;
                q.next = q.first;
 
                p.first.next = p.next;
                p.next.first = p.first;
                p.next = p.first;
 
                p.first = q.first;
                q.first = p.next;
 
                p.next = p.first;
                q.next = q.first;
 
                q.next = q.next.next;
                q.first.next = q;
                q.next.first = q;
 
                p.next = p.next.next;
                p.first.next = p;
                p.next.first = p;
            }
        }
    }
 
    static public void Main()
    {
 
        GFG list = new GFG();
 
        // function calls for inserting
        // at the end of the list
        list.AddLast(10);
        list.AddLast(20);
        list.AddLast(30);
        list.AddLast(40);
        list.AddLast(50);
        list.AddLast(60);
 
        Console.WriteLine("Before swapping:");
        // print list before swapping the nodes
        list.printList();
        Console.WriteLine();
 
        // function call for swapping Kth nodes
        list.swapKthNodes(1);
 
        Console.WriteLine(
            "After swapping nodes for k = 1:");
        // print list after swapping the nodes
        list.printList();
        Console.WriteLine();
 
        list.swapKthNodes(2);
        Console.WriteLine(
            "After swapping nodes for k = 2:");
        list.printList();
        Console.WriteLine();
 
        list.swapKthNodes(3);
        Console.WriteLine(
            "After swapping nodes for k = 3 (middle):");
        list.printList();
        Console.WriteLine();
    }
}
 
// This code is contributed by lokesh (lokeshmvs21).

Javascript

// Javascript code
class Node {
    constructor(data) {
        this.data = data;
        this.first = null;
        this.next = null;
    }
}
 
// function for inserting new node at the
// end of the list using last pointer
function AddLast(data, head, last) {
    let temp = new Node(data);
    if (!head) {
        head = temp;
        last = temp;
    }
    else {
        last.next = temp;
        temp.first = last;
        last = temp;
    }
    return [head, last];
}
 
// function for printing the doubly linked list
function printList(head) {
    let p = head;
    while (p) {
        console.log(`${p.data}<->`);
        p = p.next;
    }
    console.log("NULL");
}
 
// function for swapping Kth node from
// beginning with Kth node from the end
function swapKthNodes(head, last, k) {
    let count = 1;
    let p = head, q = last;
    // case 1: to swap the start and end nodes
    // case 1 figure
    if (k == 1) {
        q.first.next = p;
        p.first = q.first;
 
        q.next = p.next;
        p.next.first = q;
 
        // change these links to NULL to the break circular
        // link
        p.next = null;
        q.first = null;
 
        head = q;
        last = p;
        return [head, last];
    }
    else {
        while (p != null && q != null && count < k) {
            count++;
            p = p.next;
            q = q.first;
        }
 
        // case 3: if the nodes to be swapped are the middle
        // nodes given in the figure
        if (p.next == q) {
            p.first.next = p.next.next;
            q.next.first = p.first;
 
            p.next = p.first;
            q.first = q.next = p.first;
 
            q.next = p;
            p.next.next.first = p;
            p.next = p.first.next;
 
            p.first.next = q;
            p.first = q;
        }
        // case 2: other than middle nodes
        // given in case 2 figure
        else {
            q.first.next = q.next;
            q.next.first = q.first;
            q.next = q.first;
 
            p.first.next = p.next;
            p.next.first = p.first;
            p.next = p.first;
 
            p.first = q.first;
            q.first = p.next;
 
            p.next = p.first;
            q.next = q.first;
 
            q.next = q.next.next;
            q.first.next = q;
            q.next.first = q;
 
            p.next = p.next.next;
            p.first.next = p;
            p.next.first = p;
        }
    }
    return [head, last];
}
 
// Driver function
// head pointer for pointing to start of the linked list
// last pointer for pointing to last node of the linked
// list
let head = null, last = null;
 
// function calls for inserting
// at the end of the list
[head, last] = AddLast(10, head, last);
[head, last] = AddLast(20, head, last);
[head, last] = AddLast(30, head, last);
[head, last] = AddLast(40, head, last);
[head, last] = AddLast(50, head, last);
[head, last] = AddLast(60, head, last);
 
console.log("Before swapping:");
// print list before swapping the nodes
printList(head);
console.log();
 
// function call for swapping Kth nodes
[head, last] = swapKthNodes(head, last, 1);
 
console.log("After swapping nodes for k = 1:");
// print list after swapping the nodes
printList(head);
console.log();
 
[head, last] = swapKthNodes(head, last, 2);
console.log("After swapping nodes for k = 2:");
printList(head);
console.log();
 
[head, last] = swapKthNodes(head, last, 3);
console.log("After swapping nodes for k = 3 (middle):");
printList(head);
console.log();
 
// This code is contributed by akashish__

Output

Before swapping:
10<->20<->30<->40<->50<->60<->NULL

After swapping nodes for k = 1:
60<->20<->30<->40<->50<->10<->NULL

After swapping nodes for k = 2:
60<->50<->30<->40<->20<->10<->NULL

After swapping nodes for k = 3 (middle):
60<->50<->40<->30<->20<->10<->NULL

Time complexity: O(N) where N is number of nodes in linked list
Auxiliary Space: O(1)

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