Q:

Program to swap the last element of the singly linked list from the first one

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robaa
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2022-11-10
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Explanation

In this program we need to swap the last node of the singly linked list with the first node such that first node will become the last node and last node will become the first node.

Consider the above example; node 1 represents the head of the list and node 4 represent the last node. To swap the first node with the last node, we will iterate through the list such that index will point to second last node and current will point to the last node. Node temp will point to head. Then, make current (last node) as the new head of the list. Now, move the entire list after the old head and attach it after new head. Finally, add temp (old head node) after index node (second last node).

Algorithm

  1. Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
  2. Create another class Swap which has two attributes: head and tail.
  3. addNode() will add a new node to the list:
    1. Create a new node.
    2. It first checks, whether the head is equal to null which means the list is empty.
    3. If the list is empty, both head and tail will point to a newly added node.
    4. If the list is not empty, the new node will be added to end of the list such that tail's next will point to a newly added node. This new node will become the new tail of the list.
  4. SwapFirstWithLast() will swap the first node with the last node:
    1. If the list is empty, return from the function.
    2. If the list is not empty, traverse through the list such that node current will point to the last node of the list and index will point to second last node.
    3. Check if the list contains only one node, then swapping is not possible.
    4. If the list contains only two nodes then, swap head node with current using node temp.
    5. Else, the temp will point to head, and current which was pointing to the last node will become the new head of the list.
    6. Move the list except for the old head node and attach it after new head, i.e. head.next = temp.next
    7. Now add the temp (first) node after index node to make it last node of the list and its next node will be null.
  5. display() will display the nodes present in the list:
    1. Define a node current which will initially point to the head of the list.
    2. Traverse through the list till current points to null.
    3. Display each node by making current to point to node next to it in each iteration.

Input:

 

#Add nodes to the list  

sList.addNode(1);  

sList.addNode(2);  

sList.addNode(3);  

sList.addNode(4);  

Output:

Originals list: 1 2 3 4
List after swapping the first node with last: 4 2 3 1
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robaa
2022-11-10
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Python

#Represent a node of the singly linked list  
class Node:  
    def __init__(self,data):  
        self.data = data;  
        self.next = None;  
          
class Swap:  
    #Represent the head of the singly linked list  
    def __init__(self):  
        self.head = None;  
          
    #addNode() will add a new node to the list  
    def addNode(self, data):  
        #Create a new node  
        newNode = Node(data);  
          
        #Checks if the list is empty  
        if(self.head == None):  
            #If list is empty, head will point to new node  
            self.head = newNode;  
        else:  
            current = self.head;  
            while(current.next != None):  
                current = current.next;  
            #newNode will be added after last node of the list  
            current.next = newNode;  
              
    #swapLastWithFirst() will swap head node with the last node of the list  
    def swapLastWithFirst(self):  
        current = self.head;  
        temp = None;  
        index = None;  
          
        #If list is empty, then display the list as it is  
        if(self.head == None):  
            return;  
        else:  
            #After the loop, current will point to last element and index will point to second last element  
            while(current.next != None):  
                index = current;  
                current = current.next;  
                  
            #If list contains only one node, then display list as it is  
            if(self.head == current):  
                return;  
                  
            #If list contains only two nodes, then swap the head node with current node  
            elif(self.head.next == current):  
                temp = self.head;  
                #head will point to last node i.e. current  
                self.head = current;  
                #node next to new head will be the last node  
                self.head.next = temp;  
                #Node next to last element will be None  
                temp.next = None;  
            else:  
                temp = self.head;  
                #head will point to last node i.e. current  
                self.head = current;  
                #Detach the list from previous head and add it after new head  
                self.head.next = temp.next;  
                #Previous head will become last node of the list  
                index.next = temp;  
                #Node next to last element will be None  
                temp.next = None;  
              
    #display() will display all the nodes present in the list  
    def display(self):  
        #Node current will point to head  
        current = self.head;  
          
        if(self.head == None):  
            print("List is empty");  
            return;  
        while(current != None):  
            #Prints each node by incrementing pointer  
            print(current.data ),  
            current = current.next;  
        print "";  
   
sList = Swap();  
          
#Add nodes to the list  
sList.addNode(1);  
sList.addNode(2);  
sList.addNode(3);  
sList.addNode(4);  
   
print("Originals list: ");  
sList.display();  
   
#Swaps Last node with first node  
sList.swapLastWithFirst();  
   
print("List after swapping the first node with last: ");  
sList.display();

 

Output:

 Originals list: 
1 2 3 4 
List after swapping the first node with last:
4 2 3 1

 

C

#include <stdio.h>  
   
//Represent a node of the singly linked list  
struct node{  
    int data;  
    struct node *next;  
};      
   
//Represent the head of the singly linked list  
struct node *head = NULL;  
   
//addNode() will add a new node to the list  
void addNode(int data) {  
    //Create a new node  
    struct node *newNode = (struct node*)malloc(sizeof(struct node));  
    newNode->data = data;  
    newNode->next = NULL;  
      
    //Checks if the list is empty  
    if(head == NULL) {  
        //If list is empty, head will point to new node  
        head = newNode;  
    }  
    else {  
        struct node *current = head;  
        while(current->next != NULL) {  
            current = current->next;  
        }  
        //newNode will be added after last node of the list  
        current->next = newNode;  
    }  
}  
   
//swapLastWithFirst() will swap head node with the last node of the list  
void swapLastWithFirst() {  
    struct node *current = head, *temp = NULL, *index = NULL;  
      
    //If list is empty, then display the list as it is  
    if(head == NULL) {  
        return;  
    }  
    else {  
        //After the loop, current will point to last element and index will point to second last element  
        while(current->next != NULL) {  
            index = current;  
            current = current->next;  
        }  
          
        //If list contains only one node, then display list as it is  
        if(head == current) {  
            return;  
        }  
        //If list contains only two nodes, then swap the head node with current node  
        else if(head->next == current) {  
            temp = head;  
            //head will point to last node i.e. current  
            head = current;  
            //node next to new head will be the last node  
            head->next = temp;  
            //Node next to last element will be null  
            temp->next = NULL;  
        }  
        else {  
            temp = head;  
            //head will point to last node i.e. current  
            head = current;  
            //Detach the list from previous head and add it after new head  
            head->next = temp->next;  
            //Previous head will become last node of the list  
            index->next = temp;  
            //Node next to last element will be null  
            temp->next = NULL;  
        }  
    }  
}  
      
//display() will display all the nodes present in the list  
void display() {  
    //Node current will point to head  
    struct node *current = head;  
      
    if(head == NULL) {  
        printf("List is empty\n");  
        return;  
    }  
    while(current != NULL) {  
        //Prints each node by incrementing pointer  
        printf("%d ", current->data);  
        current = current->next;  
    }  
    printf("\n");  
}  
      
int main()  
{  
    //Add nodes to the list  
    addNode(1);  
    addNode(2);  
    addNode(3);  
    addNode(4);  
   
    printf("Originals list: \n");  
    display();  
      
    //Swaps Last node with first node  
    swapLastWithFirst();  
      
    printf("List after swapping the first node with last: \n");  
    display();  
   
    return 0;  
}

 

Output:

Originals list: 
1 2 3 4 
List after swapping the first node with last:
4 2 3 1

 

JAVA

public class Swap {  
      
    //Represent a node of the singly linked list  
    class Node{  
        int data;  
        Node next;  
          
        public Node(int data) {  
            this.data = data;  
            this.next = null;  
        }  
    }  
   
    //Represent the head of the singly linked list  
    public Node head = null;  
      
    //addNode() will add a new node to the list  
    public void addNode(int data) {  
        //Create a new node  
        Node newNode = new Node(data);  
          
        //Checks if the list is empty  
        if(head == null) {  
            //If list is empty, head will point to new node  
            head = newNode;  
        }  
        else {  
            Node current = head;  
            while(current.next != null) {  
                current = current.next;  
            }  
            //newNode will be added after last node of the list  
            current.next = newNode;  
        }  
    }  
      
    //swapLastWithFirst() will swap head node with the last node of the list  
    public void swapLastWithFirst() {  
        Node current = head, temp = null, index = null;  
          
        //If list is empty, then display the list as it is  
        if(head == null) {  
            return;  
        }  
        else {  
            //After the loop, current will point to last element and index will point to second last element  
            while(current.next != null) {  
                index = current;  
                current = current.next;  
            }  
              
            //If list contains only one node, then display list as it is  
            if(head == current) {  
                return;  
            }  
            //If list contains only two nodes, then swap the head node with current node  
            else if(head.next == current) {  
                temp = head;  
                //head will point to last node i.e. current  
                head = current;  
                //node next to new head will be the last node  
                head.next = temp;  
                //Node next to last element will be null  
                temp.next = null;  
            }  
            else {  
                temp = head;  
                //head will point to last node i.e. current  
                head = current;  
                //Detach the list from previous head and add it after new head  
                head.next = temp.next;  
                //Previous head will become last node of the list  
                index.next = temp;  
                //Node next to last element will be null  
                temp.next = null;  
            }  
        }  
    }  
      
    //display() will display all the nodes present in the list  
    public void display() {  
        //Node current will point to head  
        Node current = head;  
        if(head == null) {  
            System.out.println("List is empty");  
            return;  
        }  
        while(current != null) {  
            //Prints each node by incrementing pointer  
            System.out.print(current.data + " ");  
            current = current.next;  
        }  
        System.out.println();  
    }  
      
    public static void main(String[] args) {  
          
        Swap sList = new Swap();  
          
        //Add nodes to the list  
        sList.addNode(1);  
        sList.addNode(2);  
        sList.addNode(3);  
        sList.addNode(4);  
   
        System.out.println("Originals list: ");  
        sList.display();  
          
        //Swaps Last node with first node  
        sList.swapLastWithFirst();  
          
        System.out.println("List after swapping the first node with last: ");  
        sList.display();  
    }  
}

 

Output:

Originals list: 
1 2 3 4 
List after swapping the first node with last:
4 2 3 1

 

C#

using System;  
                      
public class CreateList  
{  
    //Represent a node of the singly linked list  
    public class Node<T>{  
        public T data;  
        public Node<T> next;  
          
        public Node(T value) {  
            data = value;  
            next = null;  
        }  
    }  
          
    public class Swap<T>{  
        //Represent the head of the singly linked list  
        public Node<T> head = null;               
      
        //addNode() will add a new node to the list  
        public void addNode(T data) {  
            //Create a new node  
            Node<T> newNode = new Node<T>(data);  
   
            //Checks if the list is empty  
            if(head == null) {  
                //If list is empty, head will point to new node  
                head = newNode;  
            }  
            else {  
                Node<T> current = head;  
                while(current.next != null) {  
                    current = current.next;  
                }  
                //newNode will be added after last node of the list  
                current.next = newNode;  
            }  
        }  
          
        //swapLastWithFirst() will swap head node with the last node of the list  
        public void swapLastWithFirst() {  
            Node<T> current = head, temp = null, index = null;  
   
            //If list is empty, then display the list as it is  
            if(head == null) {  
                return;  
            }  
            else {  
                //After the loop, current will point to last element and index will point to second last element  
                while(current.next != null) {  
                    index = current;  
                    current = current.next;  
                }  
   
                //If list contains only one node, then display list as it is  
                if(head == current) {  
                    return;  
                }  
                //If list contains only two nodes, then swap the head node with current node  
                else if(head.next == current) {  
                    temp = head;  
                    //head will point to last node i.e. current  
                    head = current;  
                    //node next to new head will be the last node  
                    head.next = temp;  
                    //Node next to last element will be null  
                    temp.next = null;  
                }  
                else {  
                    temp = head;  
                    //head will point to last node i.e. current  
                    head = current;  
                    //Detach the list from previous head and add it after new head  
                    head.next = temp.next;  
                    //Previous head will become last node of the list  
                    index.next = temp;  
                    //Node next to last element will be null  
                    temp.next = null;  
                }  
            }  
        }  
          
        //display() will display all the nodes present in the list  
        public void display() {  
            //Node current will point to head  
            Node<T> current = head;  
              
            if(head == null) {  
                Console.WriteLine("List is empty");  
                return;  
            }  
            while(current != null) {  
                //Prints each node by incrementing pointer  
                Console.Write(current.data + " ");  
                current = current.next;  
            }  
            Console.WriteLine();  
        }  
    }  
      
    public static void Main()  
    {  
        Swap<int> sList = new Swap<int>();  
          
        //Add nodes to the list  
        sList.addNode(1);  
        sList.addNode(2);  
        sList.addNode(3);  
        sList.addNode(4);  
   
        Console.WriteLine("Originals list: ");  
        sList.display();  
          
        //Swaps Last node with first node  
        sList.swapLastWithFirst();  
          
        Console.WriteLine("List after swapping first node with last: ");  
        sList.display();      
    }  
}

 

Output:

Originals list: 
1 2 3 4 
List after swapping first node with last: 
4 2 3 1

 

PHP

<!DOCTYPE html>  
<html>  
<body>  
<?php  
//Represent a node of singly linked list  
class Node{  
    public $data;  
    public $next;  
      
    function __construct($data){  
        $this->data = $data;  
        $this->next = NULL;  
    }  
}  
class Swap{  
    //Represent the head of the singly linked list  
    public $head;  
    function __construct(){  
        $this->head = NULL;  
    }  
      
    //addNode() will add a new node to the list  
    function addNode($data) {  
        //Create a new node  
        $newNode = new Node($data);  
          
        //Checks if the list is empty  
        if($this->head == NULL) {  
            //If list is empty, head will point to new node  
            $this->head = $newNode;  
        }  
        else {  
            $current = $this->head;  
            while($current->next != null) {  
                $current = $current->next;  
            }  
            //newNode will be added after last node of the list  
            $current->next = $newNode;  
        }  
    }  
      
    //swapLastWithFirst() will swap head node with the last node of the list  
    function swapLastWithFirst() {  
        $current = $this->head;  
        $temp = null;  
        $index = null;  
          
        //If list is empty, then display the list as it is  
        if($this->head == null) {  
            return;  
        }  
        else {  
            //After the loop, current will point to last element and index will point to second last element  
            while($current->next != null) {  
                $index = $current;  
                $current = $current->next;  
            }  
              
            //If list contains only one node, then display list as it is  
            if($this->head == $current) {  
                return;  
            }  
            //If list contains only two nodes, then swap the head node with current node  
            else if($this->head->next == $current) {  
                $temp = $this->head;  
                //head will point to last node i.e. current  
                $this->head = $current;  
                //node next to new head will be the last node  
                $this->head->next = $temp;  
                //Node next to last element will be null  
                $temp->next = null;  
            }  
            else {  
                $temp = $this->head;  
                //head will point to last node i.e. current  
                $this->head = $current;  
                //Detach the list from previous head and add it after new head  
                $this->head->next = $temp->next;  
                //Previous head will become last node of the list  
                $index->next = $temp;  
                //Node next to last element will be null  
                $temp->next = null;  
            }  
        }  
    }  
      
    //display() will display all the nodes present in the list  
    function display() {  
        //Node current will point to head  
        $current = $this->head;  
          
        if($this->head == NULL) {  
            print("List is empty <br>");  
            return;  
        }  
        while($current != NULL) {  
            //Prints each node by incrementing pointer  
            print($current->data . " ");  
            $current = $current->next;  
        }  
        print("<br>");  
    }  
}  
      
$sList = new Swap();  
          
//Add nodes to the list  
$sList->addNode(1);  
$sList->addNode(2);  
$sList->addNode(3);  
$sList->addNode(4);  
   
print("Originals list: <br>");  
$sList->display();  
   
//Swaps Last node with first node  
$sList->swapLastWithFirst();  
   
print("List after swapping first node with last: <br>");  
$sList->display();  
?>  
</body>  
</html>

 

Output:

Originals list: 
1 2 3 4 
List after swapping first node with last: 
4 2 3 1

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