LinkedList AddAfter method in C#

The AddAfter method in C# LinkedList<T> allows you to insert a new node immediately after a specified existing node. This method provides precise control over node placement within the linked list structure.

Syntax

The AddAfter method has two overloads −

public LinkedListNode<T> AddAfter(LinkedListNode<T> node, T value)

public void AddAfter(LinkedListNode<T> node, LinkedListNode<T> newNode)

Parameters

• node: The existing node after which the new node will be inserted

• value: The value to be stored in the new node (first overload)

• newNode: An existing node to be inserted (second overload)

Return Value

The first overload returns a LinkedListNode<T> representing the newly created node. The second overload returns void.

Using AddAfter with Value

Example

using System;
using System.Collections.Generic;

class Demo {
   static void Main() {
      int[] num = {1, 2, 3, 4, 5};
      LinkedList<int> list = new LinkedList<int>(num);
      
      Console.WriteLine("Original LinkedList:");
      foreach (var n in list) {
         Console.WriteLine(n);
      }
      
      // Find the node with value 3
      LinkedListNode<int> targetNode = list.Find(3);
      
      // Add new node with value 10 after node containing 3
      list.AddAfter(targetNode, 10);
      
      Console.WriteLine("\nLinkedList after adding 10 after node 3:");
      foreach (var n in list) {
         Console.WriteLine(n);
      }
   }
}

The output of the above code is −

Original LinkedList:
1
2
3
4
5

LinkedList after adding 10 after node 3:
1
2
3
10
4
5

Using AddAfter with Node Reference

Example

using System;
using System.Collections.Generic;

class Demo {
   static void Main() {
      LinkedList<string> cities = new LinkedList<string>();
      cities.AddLast("New York");
      cities.AddLast("London");
      cities.AddLast("Tokyo");
      
      // Get reference to the last node
      var lastNode = cities.Last;
      
      // Add a node after the last node
      var newNode = cities.AddAfter(lastNode, "Paris");
      
      // Add another node after the newly added node
      cities.AddAfter(newNode, "Berlin");
      
      Console.WriteLine("Cities in LinkedList:");
      foreach (var city in cities) {
         Console.WriteLine(city);
      }
   }
}

The output of the above code is −

Cities in LinkedList:
New York
London
Tokyo
Paris
Berlin

Common Use Cases

• Inserting elements at specific positions based on node references rather than indices

• Building ordered lists where new elements must be placed after certain existing elements

• Implementing algorithms that require insertion at arbitrary positions during traversal

Conclusion

The AddAfter method provides efficient insertion of nodes at specific positions in a LinkedList<T>. It requires a reference to an existing node and allows precise control over the list structure without the need for index-based operations.