Program To Insert A New Node At The Beginning Of The Singly Linked List

Explanation

In this program, we will create a singly linked list and add a new node at the beginning of the list. To accomplish this task, we will store head to a temporary node temp. Make newly added node as the new head of the list. Then, add temp (old head) after new head.

Consider the above list; node 1 represents the head of the original list. Let node New be the new node which needs to be added at the beginning of the list. Node temp will point to head, i.e. 1. Make New as the new head of the list and add temp after new head such that node next to New will be 1.

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 InsertStart which has two attributes: head and tail.
addAtStart() will add a new node to the beginning of the list:
1. It first checks, whether the head is equal to null which means the list is empty.
2. If the list is empty, both head and tail will point to a newly added node.
3. If the list is not empty then, create temporary node temp will point to head.
4. Add the new node as head of the list.
5. Temp which was pointing to the old head will be added after the new head.
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 InsertStart:      #Represent the head and tail of the singly linked list      def __init__(self):          self.head = None;          self.tail = None;                #addAtStart() will add a new node to the beginning of the list      def addAtStart(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:              #Node temp will point to head              temp = self.head;              #newNode will become new head of the list              self.head = newNode;              #Node temp(previous head) will be added after new head              self.head.next = temp;                    #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;                        print(“Adding nodes to the start of the list: “);          while(current != None):              #Prints each node by incrementing pointer              print(current.data ),              current = current.next;              sList = InsertStart();     #Adding 1 to the list  sList.addAtStart(1);  sList.display();  #Adding 2 to the list  sList.addAtStart(2);  sList.display();  #Adding 3 to the list  sList.addAtStart(3);  sList.display();  #Adding 4 to the list  sList.addAtStart(4);  sList.display();  

Output:

Adding nodes to the start of the list:   1   Adding nodes to the start of the list:   2 1   Adding nodes to the start of the list:   3 2 1   Adding nodes to the start of the list:   4 3 2 1

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;     //addAtStart() will add a new node to the beginning of the list  void addAtStart(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 {          //Node temp will point to head          struct node *temp = head;          //newNode will become new head of the list          head = newNode;          //Node temp(previous head) will be added after new head          head->next = temp;      }  }        //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;      }      printf(“Adding nodes to the start of the list: n”);      while(current != NULL) {          //Prints each node by incrementing pointer          printf(“%d “, current->data);          current = current->next;      }      printf(“n”);  }        int main()  {      //Adding 1 to the list      addAtStart(1);      display();            //Adding 2 to the list      addAtStart(2);      display();            //Adding 3 to the list      addAtStart(3);      display();            //Adding 4 to the list      addAtStart(4);      display();         return 0;  }  

Output:

Adding nodes to the start of the list:   1   Adding nodes to the start of the list:   2 1   Adding nodes to the start of the list:   3 2 1   Adding nodes to the start of the list:   4 3 2 1

JAVA

  public class InsertStart {            //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;            //addAtStart() will add a new node to the beginning of the list      public void addAtStart(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 {              //Node temp will point to head              Node temp = head;              //newNode will become new head of the list              head = newNode;              //Node temp(previous head) will be added after new head              head.next = temp;          }      }            //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;          }          System.out.println(“Adding nodes to the start of the list: “);          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) {                    InsertStart sList = new InsertStart();                    //Adding 1 to the list          sList.addAtStart(1);          sList.display();                    //Adding 2 to the list          sList.addAtStart(2);          sList.display();                    //Adding 3 to the list          sList.addAtStart(3);          sList.display();                    //Adding 4 to the list          sList.addAtStart(4);          sList.display();      }  }  

Output:

Adding nodes to the start of the list:   1   Adding nodes to the start of the list:   2 1   Adding nodes to the start of the list:   3 2 1   Adding nodes to the start of the list:   4 3 2 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 InsertStart<T>{          //Represent the head and tail of the singly linked list          public Node<T> head = null;                        public Node<T> tail = null;                //addAtStart() will add a new node to the beginning of the list          public void addAtStart(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 {                  //Node temp will point to head                  Node<T> temp = head;                  //newNode will become new head of the list                  head = newNode;                  //Node temp(previous head) will be added after new head                  head.next = temp;              }          }             //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;              }              Console.WriteLine(“Adding nodes to the start of the list: “);              while(current != null) {                  //Prints each node by incrementing pointer                  Console.Write(current.data + ” “);                  current = current.next;              }              Console.WriteLine();          }      }            public static void Main()      {          InsertStart<int> sList = new InsertStart<int>();                    //Adding 1 to the list          sList.addAtStart(1);          sList.display();                    //Adding 2 to the list          sList.addAtStart(2);          sList.display();                    //Adding 3 to the list          sList.addAtStart(3);          sList.display();                    //Adding 4 to the list          sList.addAtStart(4);          sList.display();          }  }  

Output:

Adding nodes to the start of the list:   1   Adding nodes to the start of the list:   2 1   Adding nodes to the start of the list:   3 2 1   Adding nodes to the start of the list:   4 3 2 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 InsertStart{      //Represent the head and tail of the singly linked list      public $head;      public $tail;      function __construct(){          $this->head = NULL;          $this->tail = NULL;      }            //addAtStart() will add a new node to the beginning of the list      function addAtStart($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 {              //Node temp will point to head              $temp = $this->head;              //newNode will become new head of the list              $this->head = $newNode;              //Node temp(previous head) will be added after new head              $this->head->next = $temp;          }      }            //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;          }          print(“Adding nodes to the start of the list: <br>”);          while($current != NULL) {              //Prints each node by incrementing pointer              print($current->data . ” “);              $current = $current->next;          }          print(“<br>”);      }  }        $sList = new InsertStart();            //Adding 1 to the list  $sList->addAtStart(1);  $sList->display();     //Adding 2 to the list  $sList->addAtStart(2);  $sList->display();     //Adding 3 to the list  $sList->addAtStart(3);  $sList->display();     //Adding 4 to the list  $sList->addAtStart(4);  $sList->display();  ?>  </body>  </html>  

Output:

Adding nodes to the start of the list:   1   Adding nodes to the start of the list:   2 1   Adding nodes to the start of the list:   3 2 1   Adding nodes to the start of the list:   4 3 2 1

Next Topic#

Program To Insert A New Node At The Beginning Of The Singly Linked List