Program to Delete a New Node From the Beginning of the Circular Linked List

Q. Program to delete a new node from the beginning of the circular linked list.

Explanation

In this program, we will create a circular linked list and delete a node from the beginning of the list. If the list is empty, print the message “List is empty”. If the list is not empty, we will make the head to point to next node in the list, i.e., we will delete the first node.

Program to delete a new node from the beginning of the circular linked list

Circular linked list after deleting node from beginning

Program to delete a new node from the beginning of the circular linked list

Here, A represents the head of the list. We need to delete a node from the beginning of the list. So, we will remove A such that B will become new head and tail will point to the new head.

Algorithm

Define a Node class which represents a node in the list. It has two properties data and next which will point to the next node.
Define another class for creating the circular linked list and it has two nodes: head and tail. It has two methods: deleteStart() and display() .
deleteStart() will delete the node from the beginning of the list:
1. It first checks whether the head is null (empty list) then, it will return from the function as there is no node present in the list.
2. If the list is not empty, it will check whether list has only one node.
3. If the list has only one node, it will set both head and tail to null.
4. If the list has more than one node then, the head will point to the next node in the list that is, we will remove the previous head node and tail will point to the new head.
display() will show all the nodes present in the list.
1. Define a new node ‘current’ that will point to the head.
2. Print current.data till current will points to head again.
3. Current will point to the next node in the list in each iteration.

Solution

Python

  #Represents the node of list.  class Node:      def __init__(self,data):          self.data = data;          self.next = None;     class CreateList:      #Declaring head and tail pointer as null.      def __init__(self):          self.head = Node(None);          self.tail = Node(None);          self.head.next = self.tail;          self.tail.next = self.head;            #This function will add the new node at the end of the list.      def add(self,data):          newNode = Node(data);          #Checks if the list is empty.          if self.head.data is None:              #If list is empty, both head and tail would point to new node.              self.head = newNode;              self.tail = newNode;              newNode.next = self.head;          else:              #tail will point to new node.              self.tail.next = newNode;              #New node will become new tail.              self.tail = newNode;              #Since, it is circular linked list tail will point to head.              self.tail.next = self.head;            #Deletes node from the beginning of the list      def deleteStart(self):          #Checks whether list is empty          if(self.head == None):              return;          else:              #Checks whether contain only one element              #If not, head will point to next element in the list and tail will point to new head.              if(self.head != self.tail ):                  self.head = self.head.next;                  self.tail.next = self.head;              #If the list contains only one element               #then it will remove it and both head and tail will point to null              else:                  self.head = self.tail = None;                    #Displays all the nodes in the list      def display(self):          current = self.head;          if self.head is None:              print(“List is empty”);              return;          else:              #Prints each node by incrementing pointer.              print(current.data, end= ‘ ‘);              while(current.next != self.head):                  current = current.next;                  print(current.data,end=’ ‘);              print(“n”);     class CircularLinkedList:      cl = CreateList();      #Adds data to the list      cl.add(1);      cl.add(2);      cl.add(3);      cl.add(4);      #Printing original list      print(“Original List:”);      cl.display();      while(cl.head != None):          cl.deleteStart();          #Printing updated list          print(“Updated List:”);          cl.display();  

Output:

Original List:    1 2 3 4  Updated List:    2 3 4  Updated List:    3 4  Updated List:    4  Updated List:   List is empty

C

  #include <stdio.h>  #include <string.h>  #include <stdlib.h>     //Represents the node of list.  struct node{      int data;      struct node *next;  };     //Declaring head and tail pointer as null.  struct node *head = NULL;  struct node *tail = NULL;     //This function will add the new node at the end of the list.  void add(int data){      //Create new node      struct node *newNode = (struct node*)malloc(sizeof(struct node));      newNode->data = data;      //Checks if the list is empty.      if(head == NULL){          //If list is empty, both head and tail would point to new node.          head = newNode;          tail = newNode;          newNode->next = head;      }else {          //tail will point to new node.          tail->next = newNode;          //New node will become new tail.          tail = newNode;          //Since, it is circular linked list tail will point to head.          tail->next = head;      }  }     //Deletes node from the beginning of the list  void deleteStart() {      //Checks whether list is empty      if(head == NULL) {          return;      }      else {          //Checks whether contain only one element          //If not, head will point to next element in the list and tail will point to new head.          if(head != tail ) {              head = head->next;              tail->next = head;          }          //If the list contains only one element           //then it will remove it and both head and tail will point to null          else {              head = tail = NULL;          }      }  }        //This function will display the nodes of circular linked list  void display(){      struct node *current = head;      if(head == NULL){          printf(“List is empty”);      }      else{           do{               //Prints each node by incrementing pointer.              printf(“%d “, current->data);              current = current->next;          }while(current != head);          printf(“n”);      }  }        int main()  {     //Adds data to the list     add(1);     add(2);     add(3);     add(4);     //Printing original list     printf(“Original List:n “);     display();     while(head != NULL) {         deleteStart();         //Printing updated list         printf(“Updated List:n “);         display();     }          return 0;  }  

Output:

Original List:    1 2 3 4  Updated List:    2 3 4  Updated List:    3 4  Updated List:    4  Updated List:   List is empty

JAVA

  public class DeleteStart {      //Represents the node of list.      public class Node{          int data;          Node next;          public Node(int data) {              this.data = data;          }      }            //Declaring head and tail pointer as null.      public Node head = null;      public Node tail = null;            //This function will add the new node at the end of the list.      public void add(int data){          //Create new node          Node newNode = new Node(data);          //Checks if the list is empty.          if(head == null) {               //If list is empty, both head and tail would point to new node.              head = newNode;              tail = newNode;              newNode.next = head;          }          else {              //tail will point to new node.              tail.next = newNode;              //New node will become new tail.              tail = newNode;              //Since, it is circular linked list tail will point to head.              tail.next = head;          }      }            //Deletes node from the beginning of the list      public void deleteStart() {          //Checks whether list is empty          if(head == null) {              return;          }          else {              //Checks whether contain only one element              //If not, head will point to next element in the list and tail will point to new head.              if(head != tail ) {                  head = head.next;                  tail.next = head;              }              //If the list contains only one element               //then it will remove it and both head and tail will point to null              else {                  head = tail = null;              }          }      }            //Displays all the nodes in the list      public void display() {          Node current = head;          if(head == null) {              System.out.println(“List is empty”);          }          else {               do{                  //Prints each node by incrementing pointer.                  System.out.print(” “+ current.data);                  current = current.next;              }while(current != head);              System.out.println();          }      }            public static void main(String[] args) {          DeleteStart cl = new DeleteStart();          //Adds data to the list          cl.add(1);          cl.add(2);          cl.add(3);          cl.add(4);          //Printing original list          System.out.println(“Original List: “);          cl.display();          while(cl.head != null) {              cl.deleteStart();              //Printing updated list              System.out.println(“Updated List: “);              cl.display();          }      }  }  

Output:

Original List:    1 2 3 4  Updated List:    2 3 4  Updated List:    3 4  Updated List:    4  Updated List:   List is empty

C#

  using System;   namespace CircularLinkedList   {                           public class Program      {          //Represents the node of list.          public class Node<T>{              public T data;              public Node<T> next;              public Node(T value) {                  data = value;                  next = null;              }          }                    public class CreateList<T>{              public Node<T> head = null;                            public Node<T> tail = null;                            //This function will add the new node at the end of the list.              public void add(T data){                  //Create new node                  Node<T> newNode = new Node<T>(data);                  //Checks if the list is empty.                  if(head == null){                      head = newNode;                      tail = newNode;                      newNode.next = head;                  }else{                      //tail will point to new node.                      tail.next = newNode;                      //New node will become new tail.                      tail = newNode;                      //Since, it is circular linked list tail will point to head.                      tail.next = head;                  }              }                            //Deletes node from the beginning of the list              public void deleteStart() {                  //Checks whether list is empty                  if(head == null) {                      return;                  }                  else {                      //Checks whether contain only one element                      //If not, head will point to next element in the list and tail will point to new head.                      if(head != tail ) {                          head = head.next;                          tail.next = head;                      }                      //If the list contains only one element                       //then it will remove it and both head and tail will point to null                      else {                          head = tail = null;                      }                  }              }                            //Displays all the nodes in the list              public void display(){                  Node<T> current = head;                  if(head == null){                      Console.WriteLine(“List is empty”);                  }                  else{                      do{                          //Prints each node by incrementing pointer.                          Console.Write(” “+ current.data);                          current = current.next;                      }while(current != head);                      Console.WriteLine();                  }              }          }                    public static void Main()          {                        CreateList<int> cl = new CreateList<int>();          //Adds data to the list          cl.add(1);          cl.add(2);          cl.add(3);          cl.add(4);          //Printing original list          Console.WriteLine(“Original List: “);          cl.display();          while(cl.head != null) {              cl.deleteStart();              //Printing updated list              Console.WriteLine(“Updated List: “);              cl.display();          }          }          }  }  

Output:

Original List:    1 2 3 4  Updated List:    2 3 4  Updated List:    3 4  Updated List:    4  Updated List:   List is empty

PHP

  <!DOCTYPE html>  <html>  <body>  <?php  //Represents the node of list.  class Node{      public $data;      public $next;      function __construct($data){          $this->data = $data;          $this->next = NULL;      }  }  class CreateList{      //Declaring head and tail pointer as null.      public $head;      public $tail;      function __construct(){          $this->head = NULL;          $this->tail = NULL;      }      //This function will add the new node at the end of the list.      function add($data){          //Create new node          $newNode = new Node($data);          //Checks if the list is empty.          if($this->head == NULL){              //If list is empty, both head and tail would point to new node.              $this->head = $newNode;              $this->tail = $newNode;              $newNode->next = $this->head;          }          else{              //tail will point to new node.              $this->tail->next = $newNode;              //New node will become new tail.              $this->tail = $newNode;              //Since, it is circular linked list tail will point to head.              $this->tail->next = $this->head;          }      }            //Deletes node from the beginning of the list      function deleteStart() {          //Checks whether list is empty          if($this->head == NULL) {              return;          }          else {              //Checks whether contain only one element              //If not head, will point to next element in the list and tail will point to new head.              if($this->head != $this->tail ) {                  $this->head = $this->head->next;                  $this->tail->next = $this->head;              }              //If the list contains only one element               //then it will remove it and both head and tail will point to null              else {                  $this->head = $this->tail = NULL;              }          }      }            //Displays all the nodes in the list      function display() {          $current = $this->head;          if($this->head == NULL) {              echo “List is empty”;          }          else {               do{                  //Prints each node by incrementing pointer.                  echo(” $current->data”);                  $current = $current->next;              }while($current != $this->head);              echo “<br>”;          }      }     }  $cl = new CreateList();  //Adds data to the list  $cl->add(1);  $cl->add(2);  $cl->add(3);  $cl->add(4);  //Printing original list  echo “Original List:<br>”;  $cl->display();  while($cl->head != NULL) {      $cl->deleteStart();      //Printing updated list      echo “Updated List:<br>”;      $cl->display();  }  ?>  </body>  </html>  

Output:

Original List:    1 2 3 4  Updated List:    2 3 4  Updated List:    3 4  Updated List:    4  Updated List:   List is empty

Next Topic#

Q. Program to delete a new node from the beginning of the circular linked list.

Explanation

Algorithm

Solution

Python

C

JAVA

C#

PHP

Potential Energy

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