Data Structures - Linked List Other Related Topics
Data Structures - Linked List Other Related Topics

Linked List - Insert a new node at the start

In this method, a new node is inserted at the beginning of the linked list. For example - if the given List is 10->20->30 and a new element 100 is added at the start, the Linked List becomes 100->10->20->30.

Inserting a new node at the beginning of the Linked List is very easy. First, a new node with given element is created. It is then added before the head of the given Linked List that makes the newly added node to new head of the Linked List by changing the head pointer to point to the new node.

Linked List - Add Node At Start

The function push_front is created for this purpose. It is a 4-step process.

void push_front(int newElement) {
  
  //1. allocate a new node
  Node* newNode = new Node();
  
  //2. assign data element 
  newNode->data = newElement;
  
  //3. make next node of new node as head
  newNode->next = head;
  
  //4. make new node as head 
  head = newNode;   
}

void push_front(struct Node** head_ref, int newElement) {
  
  //1. allocate a new node
  struct Node* newNode;
  newNode = (struct Node*)malloc(sizeof(struct Node)); 
  
  //2. assign data element 
  newNode->data = newElement;
  
  //3. make next node of new node as head
  newNode->next = *head_ref;
  
  //4. make new node as head
  *head_ref = newNode;   
}

def push_front(self, newElement):
  
  #1 & 2. allocate a new node
  #       and assign data element
  newNode = Node(newElement)
  
  #3. make next node of new node as head
  newNode.next = self.head
  
  #4. make new node as head 
  self.head = newNode  

void push_front(int newElement) {
  
  //1. allocate a new node
  Node newNode = new Node();
  
  //2. assign data element
  newNode.data = newElement;
  
  //3. make next node of new node as head
  newNode.next = head; 
  
  //4. make new node as head
  head = newNode;   
}

public void push_front(int newElement) {
  
  //1. allocate a new node
  Node newNode = new Node();
  
  //2. assign data element 
  newNode.data = newElement;
  
  //3. make next node of new node as head
  newNode.next = head; 
  
  //4. make new node as head
  head = newNode;   
}

public function push_front($newElement) {
  
  //1. allocate a new node
  $newNode = new Node();
  
  //2. assign data element
  $newNode->data = $newElement;
  
  //3. make next node of new node as head
  $newNode->next = $this->head; 
  
  //4. make new node as head
  $this->head = $newNode;   
}

The below is a complete program that uses above discussed concept to insert new node at the start of the linked list.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }
 
    //Add new element at the start of the list
    void push_front(int newElement) {
      Node* newNode = new Node();
      newNode->data = newElement;
      newNode->next = head; 
      head = newNode;   
    }

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"The list contains: ";
        while(temp != NULL) {
          cout<<temp->data<<" ";
          temp = temp->next;
        }
        cout<<"\n";
      } else {
        cout<<"The list is empty.\n";
      }
    }   
};

// test the code 
int main() {
  LinkedList MyList;

  //Add three elements at the start of the list.
  MyList.push_front(10);
  MyList.push_front(20);
  MyList.push_front(30);
  MyList.PrintList();
  
  return 0; 
}

The above code will give the following output: 

The list contains: 30 20 10 

#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
  int data;
  struct Node* next;
};

//Add new element at the start of the list
void push_front(struct Node** head_ref, int newElement) {
  struct Node* newNode;
  newNode = (struct Node*)malloc(sizeof(struct Node));  
  newNode->data = newElement;
  newNode->next = *head_ref; 
  *head_ref = newNode;   
}

//display the content of the list
void PrintList(struct Node* head_ref) {
  struct Node* temp = head_ref;
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (temp != NULL) {
      printf("%i ",temp->data);
      temp = temp->next;  
    }
    printf("\n");
  } else {
    printf("The list is empty.\n");
  }   
}

// test the code 
int main() {
  struct Node* MyList = NULL;

  //Add three elements at the start of the list.
  push_front(&MyList, 10);
  push_front(&MyList, 20);
  push_front(&MyList, 30);
  PrintList(MyList);

  return 0; 
}

The above code will give the following output: 

The list contains: 30 20 10 

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None

#class Linked List
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the start of the list
  def push_front(self, newElement):
    newNode = Node(newElement)
    newNode.next = self.head 
    self.head = newNode   

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (temp != None):
        print(temp.data, end=" ")
        temp = temp.next
      print()
    else:
      print("The list is empty.")

# test the code                 
MyList = LinkedList()

#Add three elements at the start of the list.
MyList.push_front(10)
MyList.push_front(20)
MyList.push_front(30)
MyList.PrintList()

The above code will give the following output: 

The list contains: 30 20 10 

//node structure
class Node {
    int data;
    Node next;
};

class LinkedList {
  Node head;

  LinkedList(){
    head = null;
  }

  //Add new element at the start of the list
  void push_front(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = head; 
    head = newNode;   
  }

  //display the content of the list
  void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      System.out.print("The list contains: ");
      while(temp != null) {
        System.out.print(temp.data + " ");
        temp = temp.next;
      }
      System.out.println();
    } else {
      System.out.println("The list is empty.");
    }
  }    
};

// test the code
public class Implementation {
  public static void main(String[] args) {
    LinkedList MyList = new LinkedList();

    //Add three elements at the start of the list.
    MyList.push_front(10);
    MyList.push_front(20);
    MyList.push_front(30);
    MyList.PrintList(); 
  }
}

The above code will give the following output: 

The list contains: 30 20 10 

using System;

//node structure
class Node {
  public int data;
  public Node next;
};

class LinkedList {
  Node head;

  public LinkedList(){
    head = null;
  }
  
  //Add new element at the start of the list
  public void push_front(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = head; 
    head = newNode;   
  }

  //display the content of the list
  public void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      Console.Write("The list contains: ");
      while(temp != null) {
        Console.Write(temp.data + " ");
        temp = temp.next;
      }
      Console.WriteLine();
    } else {
      Console.WriteLine("The list is empty.");
    }
  }     
};

// test the code
class Implementation { 
  static void Main(string[] args) {
    LinkedList MyList = new LinkedList();

    //Add three elements at the start of the list.
    MyList.push_front(10);
    MyList.push_front(20);
    MyList.push_front(30);
    MyList.PrintList();   
  }
}

The above code will give the following output: 

The list contains: 30 20 10 

<?php
//node structure
class Node {
  public $data;
  public $next;
}

class LinkedList {
  public $head;

  public function __construct(){
    $this->head = null;
  }
  
  //Add element at the start of the list
  public function push_front($newElement) {
    $newNode = new Node();
    $newNode->data = $newElement;
    $newNode->next = $this->head; 
    $this->head = $newNode;   
  }

  //display the content of the list
  public function PrintList() {
    $temp = new Node();
    $temp = $this->head;
    if($temp != null) {
      echo "The list contains: ";
      while($temp != null) {
        echo $temp->data." ";
        $temp = $temp->next;
      }
      echo "\n";
    } else {
      echo "The list is empty.\n";
    }
  }   
};

// test the code 
$MyList = new LinkedList();

//Add three elements at the start of the list.
$MyList->push_front(10);
$MyList->push_front(20);
$MyList->push_front(30);
$MyList->PrintList();
?>

The above code will give the following output: 

The list contains: 30 20 10
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