Program To Delete A New Node From The Beginning Of The Singly Linked List

Explanation

In this program, we will create a singly linked list and delete a node from the beginning of the list. To accomplish this task, we need to make the head pointer pointing to the immediate next of the initial node which will now become the new head node of the list.

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

Consider the above example; Node was the head of the list. Make head to point to next node in the list. Now, node 1 will become the new head of the list. Thus, deleting the 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 DeleteStart 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.
deleteFromStart() will delete a node from the beginning of the list:
1. It first checks whether the head is null (empty list) then, display the message “List is empty” and return.
2. If the list is not empty, it will check whether the 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 and delete the old head node.
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 DeleteStart:      #Represent the head and tail of the singly linked list      def __init__(self):          self.head = None;          self.tail = 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, both head and tail will point to new node              self.head = newNode;              self.tail = newNode;          else:              #newNode will be added after tail such that tail’s next will point to newNode              self.tail.next = newNode;              #newNode will become new tail of the list              self.tail = newNode;                    #deleteFromStart() will delete a node from the beginning of the list      def deleteFromStart(self):                    #Checks if the list is empty          if(self.head == None):              printf(“List is emptyn”);              return;          else:              #Checks whether the list contains only one node              #If not, head will point to next node in the list and tail will point to new head.              if(self.head != self.tail):                  self.head = self.head.next;                  #If the list contains only one node                  #then, it will remove it and both head and tail will point to None              else:                  self.head = self.tail = 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, end=” “);              current = current.next;          print();     sList =  DeleteStart();     #Adds data to the list  sList.addNode(1);  sList.addNode(2);  sList.addNode(3);  sList.addNode(4);  #Printing original list  print(“Original List: “);  sList.display();     while(sList.head != None):      sList.deleteFromStart();      #Printing updated list      print(“Updated List: “);      sList.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>     //Represent a node of the singly linked list  struct node{      int data;      struct node *next;  };         //Represent the head and tail of the singly linked list  struct node *head, *tail = 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, both head and tail will point to new node          head = newNode;          tail = newNode;      }      else {          //newNode will be added after tail such that tail’s next will point to newNode          tail->next = newNode;          //newNode will become new tail of the list          tail = newNode;      }  }     //deleteFromStart() will delete a node from the beginning of the list  void deleteFromStart() {            //Checks if the list is empty      if(head == NULL) {          printf(“List is empty n”);          return;      }      else {          //Checks whether the list contains only one node          //If not, the head will point to next node in the list and tail will point to the new head.          if(head != tail) {              head = head->next;          }          //If the list contains only one node           //then, it will remove it and both head and tail will point to NULL          else {              head = tail = 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()  {      //Adds data to the list      addNode(1);      addNode(2);      addNode(3);      addNode(4);            //Printing original list      printf(“Original List: n”);      display();            while(head != NULL) {          deleteFromStart();          //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 {            //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 and tail of the singly linked list      public Node head = null;      public Node tail = 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, both head and tail will point to new node              head = newNode;              tail = newNode;          }          else {              //newNode will be added after tail such that tail’s next will point to newNode              tail.next = newNode;              //newNode will become new tail of the list              tail = newNode;          }      }            //deleteFromStart() will delete a node from the beginning of the list      public void deleteFromStart() {                    //Checks if the list is empty          if(head == null) {              System.out.println(“List is empty”);              return;          }          else {              //Checks whether the list contains only one node              //If not, the head will point to next node in the list and tail will point to the new head.              if(head != tail) {                  head = head.next;              }              //If the list contains only one node               //then, it will remove it and both head and tail will point to null              else {                  head = tail = 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) {                    DeleteStart sList = new DeleteStart();                    //Adds data to the list          sList.addNode(1);          sList.addNode(2);          sList.addNode(3);          sList.addNode(4);                    //Printing original list          System.out.println(“Original List: “);          sList.display();                    while(sList.head != null) {              sList.deleteFromStart();              //Printing updated list              System.out.println(“Updated List: “);              sList.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;                        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 DeleteStart<T>{          //Represent the head and tail of the singly linked list          public Node<T> head = null;                        public Node<T> tail = 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, both head and tail will point to new node                  head = newNode;                  tail = newNode;              }              else {                  //newNode will be added after tail such that tail’s next will point to newNode                  tail.next = newNode;                  //newNode will become new tail of the list                  tail = newNode;              }          }                //deleteFromStart() will delete a node from the beginning of the list          public void deleteFromStart() {                 //Checks if the list is empty              if(head == null) {                  Console.WriteLine(“List is empty”);                  return;              }              else {                  //Checks whether the list contains only one node                  //If not, the head will point to next node in the list and tail will point to the new head.                  if(head != tail) {                      head = head.next;                  }                  //If the list contains only one node                   //then, it will remove it and both head and tail will point to null                  else {                      head = tail = 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()      {          DeleteStart<int> sList = new DeleteStart<int>();                    //Adds data to the list          sList.addNode(1);          sList.addNode(2);          sList.addNode(3);          sList.addNode(4);                    //Printing original list          Console.WriteLine(“Original List: “);          sList.display();                    while(sList.head != null) {              sList.deleteFromStart();              //Printing updated list              Console.WriteLine(“Updated List: “);              sList.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  //Represent a node of singly linked list  class Node{      public $data;      public $next;            function __construct($data){          $this->data = $data;          $this->next = NULL;      }  }  class DeleteStart{      //Represent the head and tail of the singly linked list      public $head;      public $tail;      function __construct(){          $this->head = NULL;          $this->tail = NULL;      }            //addNode() will add a new node to the list      function addNode($data) {          //Create a new node          $newNode = new Node($data);                    //Checks if the list is empty          if($this->head == null) {              //If list is empty, both head and tail will point to new node              $this->head = $newNode;              $this->tail = $newNode;          }          else {              //newNode will be added after tail such that tail’s next will point to newNode              $this->tail->next = $newNode;              //newNode will become new tail of the list              $this->tail = $newNode;          }      }            //deleteFromStart() will delete a node from the beginning of the list      function deleteFromStart() {                    //Checks if the list is empty          if($this->head == null) {              print(“List is empty <br>”);              return;          }          else {              //Checks whether the list contains only one node              //If not, head will point to next node in the list and tail will point to new head.              if($this->head != $this->tail) {                  $this->head = $this->head->next;              }              //If the list contains only one node               //then, it will remove it and both head and tail will point to null              else {                  $this->head = $this->tail = 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 DeleteStart();            //Adds data to the list  $sList->addNode(1);  $sList->addNode(2);  $sList->addNode(3);  $sList->addNode(4);     //Printing original list  print(“Original List: <br>”);  $sList->display();     while($sList->head != null) {      $sList->deleteFromStart();      //Printing updated list      print(“Updated List: <br>”);      $sList->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

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Program To Delete A New Node From The Beginning Of The Singly Linked List