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Added Circular Linked List Data Structure
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‎DataStructures.Tests/LinkedList/CircularLinkedListTests.cs‎

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using System;
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using DataStructures.LinkedList.CircularLinkedList;
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using NUnit.Framework;
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namespace DataStructures.Tests.LinkedList;
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[TestFixture]
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public static class CircularLinkedListTests
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{
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[Test]
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public static void TestInsertAtBeginning()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtBeginning(10);
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cll.InsertAtBeginning(20);
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cll.InsertAtBeginning(30);
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Assert.That("30 20 10", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestInsertAtEnd()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtEnd(10);
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cll.InsertAtEnd(20);
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cll.InsertAtEnd(30);
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Assert.That("10 20 30", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestInsertAfter()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtEnd(10);
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cll.InsertAtEnd(20);
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cll.InsertAtEnd(30);
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cll.InsertAfter(20, 25);
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Assert.That("10 20 25 30", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestDeleteNode()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtEnd(10);
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cll.InsertAtEnd(20);
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cll.InsertAtEnd(30);
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cll.DeleteNode(20);
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Assert.That("10 30", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestDisplay()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtEnd(10);
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cll.InsertAtEnd(20);
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cll.InsertAtEnd(30);
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Assert.That("10 20 30", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestDeleteFromEmptyList()
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{
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var cll = new CircularLinkedList<int>();
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cll.DeleteNode(10);
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Assert.That(cll.IsEmpty(), Is.EqualTo(true));
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}
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[Test]
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public static void TestInsertInEmptyList()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtBeginning(10);
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Assert.That("10", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestInsertAfterOnNonExistingValue()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtEnd(10);
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cll.InsertAfter(99, 25); // 99 does not exist
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Assert.That("10", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestDeleteOnlyNode()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtBeginning(10);
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cll.DeleteNode(10);
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Assert.That(cll.IsEmpty(), Is.EqualTo(true));
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}
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[Test]
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public static void TestDeleteHeadNode()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtEnd(10);
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cll.InsertAtEnd(20);
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cll.InsertAtEnd(30);
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cll.DeleteNode(10);
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Assert.That("20 30", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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[Test]
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public static void TestDeleteTailNode()
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{
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var cll = new CircularLinkedList<int>();
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cll.InsertAtEnd(10);
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cll.InsertAtEnd(20);
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cll.InsertAtEnd(30);
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cll.DeleteNode(30);
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Assert.That("10 20", Is.EqualTo(GetDisplayOutput(cll).Trim()));
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}
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/// <summary>
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/// Helper method to capture the output of the Display method for assertions.
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/// </summary>
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/// <param name="list">The CircularLinkedList instance.</param>
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/// <returns>A string representation of the list.</returns>
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private static string GetDisplayOutput(CircularLinkedList<int> list)
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{
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// Save the original output (the default Console output stream)
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var originalConsoleOut = Console.Out;
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// Use a StringWriter to capture Console output
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using (var sw = new System.IO.StringWriter())
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{
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try
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{
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// Redirect Console output to StringWriter
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Console.SetOut(sw);
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// Call the method that outputs to the console
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list.Display();
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// Return the captured output
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return sw.ToString();
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}
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finally
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{
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// Restore the original Console output stream
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Console.SetOut(originalConsoleOut);
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}
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}
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}
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}

‎DataStructures/LinkedList/CircularLinkedList/CircularLinkedList.cs‎

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using System;
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namespace DataStructures.LinkedList.CircularLinkedList
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{
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/// <summary>
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/// CircularLinkedList.
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/// @author Mohit Singh. <a href="https://github.com/mohit-gogitter">mohit-gogitter</a>
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/// </summary>
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/// <typeparam name="T">The generic type parameter.</typeparam>
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public class CircularLinkedList<T>
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{
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/// <summary>
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/// Points to the last node in the Circular Linked List.
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/// </summary>
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private CircularLinkedListNode<T>? tail;
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/// <summary>
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/// Initializes a new instance of the <see cref="CircularLinkedList{T}"/> class.
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/// </summary>
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public CircularLinkedList()
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{
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tail = null;
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}
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/// <summary>
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/// Determines whether the Circular Linked List is empty.
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/// </summary>
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/// <returns>True if the list is empty; otherwise, false.</returns>
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public bool IsEmpty()
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{
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return tail == null;
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}
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/// <summary>
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/// Inserts a new node at the beginning of the Circular Linked List.
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/// </summary>
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/// <param name="data">The data to insert into the new node.</param>
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public void InsertAtBeginning(T data)
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{
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var newNode = new CircularLinkedListNode<T>(data);
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if (IsEmpty())
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{
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tail = newNode;
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tail.Next = tail;
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}
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else
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{
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newNode.Next = tail!.Next;
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tail.Next = newNode;
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}
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}
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/// <summary>
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/// Inserts a new node at the end of the Circular Linked List.
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/// </summary>
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/// <param name="data">The data to insert into the new node.</param>
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public void InsertAtEnd(T data)
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{
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var newNode = new CircularLinkedListNode<T>(data);
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if (IsEmpty())
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{
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tail = newNode;
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tail.Next = tail;
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}
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else
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{
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newNode.Next = tail!.Next;
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tail.Next = newNode;
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tail = newNode;
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}
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}
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/// <summary>
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/// Inserts a new node after a specific value in the list.
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/// </summary>
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/// <param name="value">The value to insert the node after.</param>
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/// <param name="data">The data to insert into the new node.</param>
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public void InsertAfter(T value, T data)
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{
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if (IsEmpty())
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{
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Console.WriteLine("List is empty.");
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return;
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}
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var current = tail!.Next;
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do
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{
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if (current!.Data!.Equals(value))
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{
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var newNode = new CircularLinkedListNode<T>(data);
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newNode.Next = current.Next;
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current.Next = newNode;
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if (current == tail)
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{
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tail = newNode;
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}
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return;
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}
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current = current.Next;
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}
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while (current != tail.Next);
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Console.WriteLine($"Node with value {value} not found.");
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}
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/// <summary>
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/// Deletes a node with a specific value from the list.
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/// </summary>
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/// <param name="value">The value of the node to delete.</param>
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public void DeleteNode(T value)
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{
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if (IsEmpty())
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{
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Console.WriteLine("List is empty.");
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return;
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}
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var current = tail!.Next;
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var previous = tail;
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do
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{
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if (current!.Data!.Equals(value))
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{
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if (current == tail && current.Next == tail)
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{
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tail = null;
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}
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else if (current == tail)
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{
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previous!.Next = tail.Next;
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tail = previous;
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}
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else if (current == tail.Next)
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{
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tail.Next = current.Next;
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}
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else
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{
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previous!.Next = current.Next;
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}
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Console.WriteLine($"Node with value {value} deleted.");
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return;
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}
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previous = current;
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current = current.Next;
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}
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while (current != tail!.Next);
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Console.WriteLine($"Node with value {value} not found.");
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}
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/// <summary>
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/// Displays the contents of the Circular Linked List.
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/// </summary>
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public void Display()
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{
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if (IsEmpty())
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{
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Console.WriteLine("List is empty.");
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return;
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}
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CircularLinkedListNode<T>? current = tail!.Next;
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do
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{
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Console.Write($"{current!.Data} ");
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current = current.Next;
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}
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while (current != tail!.Next);
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Console.WriteLine();
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}
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}
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}

‎DataStructures/LinkedList/CircularLinkedList/CircularLinkedListNode.cs‎

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namespace DataStructures.LinkedList.CircularLinkedList
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{
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/// <summary>
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/// Represents a node in the Circular Linked List.
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/// Each node contains generic data and a reference to the next node.
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/// </summary>
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/// <typeparam name="T">The type of the data stored in the node.</typeparam>
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/// <remarks>
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/// Initializes a new instance of the <see cref="CircularLinkedListNode{T}"/> class.
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/// </remarks>
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/// <param name="data">The data to be stored in the node.</param>
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public class CircularLinkedListNode<T>(T data)
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{
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/// <summary>
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/// Gets or sets the data for the node.
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/// </summary>
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public T Data { get; set; } = data;
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/// <summary>
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/// Gets or sets the reference to the next node in the list.
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/// </summary>
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public CircularLinkedListNode<T>? Next { get; set; } = null;
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}
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}

‎README.md‎

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* [Singly Linked List](./DataStructures/LinkedList/SinglyLinkedList/SinglyLinkedList.cs)
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* [Doubly Linked List](./DataStructures/LinkedList/DoublyLinkedList/DoublyLinkedList.cs)
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* [Skip List](./DataStructures/LinkedList/SkipList/SkipList.cs)
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* [Circular Linked List](./DataStructures/LinkedList/CircularLinkedList/CircularLinkedList.cs)
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* [Graph](./DataStructures/Graph)
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* [Directed Weighted Graph Via Adjacency Matrix](./DataStructures/Graph/DirectedWeightedGraph.cs)
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* [Disjoint Set](./DataStructures/DisjointSet)

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