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: 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:

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:

• https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.linkedlist-1.addfirst?view=netframework-4.7.2