Program To Swap The Last Element Of The Singly Linked List From The First One

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.

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

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

Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
Create another class Swap which has two attributes: head and tail.
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.
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.
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.

Solution

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 emptyn”);          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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Program To Swap The Last Element Of The Singly Linked List From The First One