C# Program to add a node after the given node in a Linked List

A LinkedList in C# is a doubly linked list that allows efficient insertion and removal of elements at any position. The AddAfter() method inserts a new node immediately after a specified existing node in the list.

Syntax

Following is the syntax for the AddAfter() method −

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

Parameters

• node − The LinkedListNode after which to insert a new node containing value.

• value − The value to add to the LinkedList.

Return Value

The method returns the new LinkedListNode<T> containing the specified value.

Using AddAfter with Node Reference

Example

using System;
using System.Collections.Generic;

class Demo {
   static void Main() {
      string[] students = {"Beth", "Jennifer", "Amy", "Vera"};
      LinkedList<string> list = new LinkedList<string>(students);
      
      Console.WriteLine("Original LinkedList:");
      foreach (var stu in list) {
         Console.WriteLine(stu);
      }

      // adding a node at the end
      var newNode = list.AddLast("Emma");

      // adding a new node after the node added above
      list.AddAfter(newNode, "Matt");

      Console.WriteLine("\nLinkedList after adding new nodes:");
      foreach (var stu in list) {
         Console.WriteLine(stu);
      }
   }
}

The output of the above code is −

Original LinkedList:
Beth
Jennifer
Amy
Vera

LinkedList after adding new nodes:
Beth
Jennifer
Amy
Vera
Emma
Matt

Using AddAfter with Find Method

You can also use the Find() method to locate an existing node and add a new node after it −

Example

using System;
using System.Collections.Generic;

class Program {
   static void Main() {
      LinkedList<int> numbers = new LinkedList<int>();
      numbers.AddLast(10);
      numbers.AddLast(20);
      numbers.AddLast(30);
      
      Console.WriteLine("Original list:");
      foreach (int num in numbers) {
         Console.Write(num + " ");
      }
      
      // Find the node with value 20 and add 25 after it
      LinkedListNode<int> foundNode = numbers.Find(20);
      if (foundNode != null) {
         numbers.AddAfter(foundNode, 25);
      }
      
      Console.WriteLine("
\nAfter adding 25 after node 20:");
      foreach (int num in numbers) {
         Console.Write(num + " ");
      }
   }
}

The output of the above code is −

Original list:
10 20 30 

After adding 25 after node 20:
10 20 25 30

Adding Multiple Nodes

Example

using System;
using System.Collections.Generic;

class MultipleNodes {
   static void Main() {
      LinkedList<string> colors = new LinkedList<string>();
      colors.AddLast("Red");
      colors.AddLast("Blue");
      
      Console.WriteLine("Initial colors:");
      foreach (string color in colors) {
         Console.WriteLine(color);
      }
      
      // Add multiple nodes after "Red"
      LinkedListNode<string> redNode = colors.Find("Red");
      colors.AddAfter(redNode, "Orange");
      colors.AddAfter(redNode, "Yellow");  // This adds Yellow right after Red
      
      Console.WriteLine("\nAfter adding Orange and Yellow:");
      foreach (string color in colors) {
         Console.WriteLine(color);
      }
   }
}

The output of the above code is −

Initial colors:
Red
Blue

After adding Orange and Yellow:
Red
Yellow
Orange
Blue

Conclusion

The AddAfter() method in C# LinkedList provides an efficient way to insert new nodes at specific positions. It requires a reference to an existing node and inserts the new node immediately after it, maintaining the doubly-linked structure of the list.