C# | Adding new node or value at the start of LinkedList<T>

LinkedList<T>.AddFirst Method is used to add a new node or value at the starting of the LinkedList<T>. There are 2 methods in the overload list of this method as follows:

  1. AddFirst(LinkedList<T>)
  2. AddFirst(T)

AddFirst(LinkedListNode<T>)

This method is used to add the specified new node at the starting of the LinkedList<T>.

Syntax:

public void AddFirst (System.Collections.Generic.LinkedListNode<T> node);

Here, node is the new LinkedListNode<T> to add at the start of the LinkedList<T>.



Exceptions:

  • ArgumentNullException : If the node is null.
  • InvalidOperationException : If the node belongs to another LinkedList<T>.

Example:

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// C# code to add new node
// at the start of LinkedList
using System;
using System.Collections;
using System.Collections.Generic;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
        // Creating a LinkedList of Integers
        LinkedList<int> myList = new LinkedList<int>();
  
        // Adding nodes in LinkedList
        myList.AddLast(2);
        myList.AddLast(4);
        myList.AddLast(6);
        myList.AddLast(6);
        myList.AddLast(6);
        myList.AddLast(8);
  
        // To get the count of nodes in LinkedList
        // before removing all the nodes
        Console.WriteLine("Total nodes in myList are : " + myList.Count);
  
        // Displaying the nodes in LinkedList
        foreach(int i in myList)
        {
            Console.WriteLine(i);
        }
  
        // Adding new node at the start of LinkedList
        // This will give error as node is null
        myList.AddFirst(5);
  
        // To get the count of nodes in LinkedList
        // after removing all the nodes
        Console.WriteLine("Total nodes in myList are : " + myList.Count);
  
        // Displaying the nodes in LinkedList
        foreach(int i in myList)
        {
            Console.WriteLine(i);
        }
    }
}

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Output:



Total nodes in myList are : 6

2

4

6

6

6

8


Unhandled Exception:

System.ArgumentNullException: Value cannot be null.

Parameter name: node



Note: 


    

  • LinkedList<T> accepts null as a valid Value for reference types and allows duplicate values. 
    • 

  • If the LinkedList<T> is empty, the new node becomes the First and the Last. 
    • 

  • This method is an O(1) operation.
    • 



AddFirst(T) Method


This method is used to add a new node containing the specified value at the start of the LinkedList<T>.


Syntax:


public System.Collections.Generic.LinkedListNode AddFirst (T value);



Here, value is the value to add at the start of the LinkedList<T>.


Return Value: The new LinkedListNode<T> containing value.


Example:











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// C# code to add new node containing 


// the specified value at the start 


// of LinkedList 


using System; 


using System.Collections; 


using System.Collections.Generic; 


  


class GFG { 


  


    // Driver code 


    public static void Main() 


    { 


        // Creating a LinkedList of Integers 


        LinkedList<int> myList = new LinkedList<int>(); 


  


        // Adding nodes in LinkedList 


        myList.AddLast(2); 


        myList.AddLast(4); 


        myList.AddLast(6); 


        myList.AddLast(6); 


        myList.AddLast(6); 


        myList.AddLast(8); 


  


        // To get the count of nodes in LinkedList 


        // before removing all the nodes 


        Console.WriteLine("Total nodes in myList are : " + myList.Count); 


  


        // Displaying the nodes in LinkedList 


        foreach(int i in myList) 


        { 


            Console.WriteLine(i); 


        } 


  


        // Adding new node containing the 


        // specified value at the start of LinkedList 


        myList.AddFirst(20); 


  


        // To get the count of nodes in LinkedList 


        // after removing all the nodes 


        Console.WriteLine("Total nodes in myList are : " + myList.Count); 


  


        // Displaying the nodes in LinkedList 


        foreach(int i in myList) 


        { 


            Console.WriteLine(i); 


        } 


    } 


} 



















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Output:


Total nodes in myList are : 6
2
4
6
6
6
8
Total nodes in myList are : 7
20
2
4
6
6
6
8



Note: 


    

  • LinkedList<T> accepts null as a valid Value for reference types and allows duplicate values. 
    • 

  • If the LinkedList<T> is empty, the new node becomes the First and the Last. 
    • 

  • This method is an O(1) operation.
    • 



Reference:






    

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