[Hacker Rank] Interview Preparation Kit: Linked Lists: Detect a Cycle. Solved ✓.

Author: Gonzalo Diaz

algorithm-exercises-csharp-test/src/hackerrank/interview_preparation_kit/linked_list/LinkedListCycle.Test.cs

@@ -0,0 +1,74 @@
+namespace algorithm_exercises_csharp.hackerrank.interview_preparation_kit;
+
+[TestClass]
+public class LinkedListCycleTest
+{
+  class LinkedListCycleTestCase
+  {
+    public string title = "";
+    public LinkedList.Node? llist;
+    public bool expected;
+  }
+
+  private static LinkedListCycleTestCase[] tests = [];
+
+  [TestInitialize]
+  public void testInitialize()
+  {
+    // Linked list sample data:
+    LinkedList.Node ll1_1 = new(1);
+    LinkedList.Node ll1_2 = new(2);
+    LinkedList.Node ll1_3 = new(3);
+    LinkedList.Node ll1_4 = new(4);
+    LinkedList.Node ll1_5 = new(5);
+
+    ll1_1.next = ll1_2;
+    ll1_2.next = ll1_3;
+    ll1_3.next = ll1_4;
+    ll1_4.next = ll1_5;
+    ll1_4.next = ll1_3; // <- cycle
+
+    LinkedList.Node ll2_1 = new(1);
+    LinkedList.Node ll2_2 = new(2);
+    LinkedList.Node ll2_3 = new(3);
+
+    ll2_1.next = ll2_2;
+    ll2_2.next = ll2_3;
+
+    tests = [
+      new()
+      {
+        title = "Sample Test case X",
+        llist = ll1_1,
+        expected = true
+      },
+      new()
+      {
+        title = "Sample Test case Y",
+        llist = ll2_1,
+        expected = false
+      }
+    ];
+  }
+
+  [TestMethod]
+  public void testLinkedListCycle()
+  {
+    bool result;
+
+    foreach (LinkedListCycleTestCase test in tests)
+    {
+      result = LinkedListCycle.hasCycle(test.llist);
+      Assert.AreEqual(
+        test.expected,
+        result,
+        String.Format(
+          "{0} testLinkedListCycle({1}) => must be: {2}",
+          test.title,
+          test.llist,
+          test.expected
+        )
+      );
+    }
+  }
+}

algorithm-exercises-csharp/src/hackerrank/interview_preparation_kit/linked_list/LinkedListCycle.cs

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+namespace algorithm_exercises_csharp.hackerrank.interview_preparation_kit;
+
+using System.Diagnostics.CodeAnalysis;
+
+public class LinkedListCycle
+{
+  [ExcludeFromCodeCoverage]
+  protected LinkedListCycle() { }
+
+  public static bool hasCycle(LinkedList.Node? head)
+  {
+    List<LinkedList.Node> llindex = [];
+
+    LinkedList.Node? node = head;
+
+    while (node != null)
+    {
+      if (llindex.Contains(node))
+      {
+        return true;
+      }
+
+      llindex.Add(node);
+      node = node.next;
+    }
+
+    return false;
+  }
+}

algorithm-exercises-csharp/src/hackerrank/interview_preparation_kit/linked_list/lib/Node.cs

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+namespace algorithm_exercises_csharp.hackerrank.interview_preparation_kit;
+
+public class LinkedList
+{
+  public class Node(int nodeData)
+  {
+    public int data { get; set; } = nodeData;
+    public Node? next { get; set; } = null;
+  }
+
+  public static void printSinglyLinkedList(Node node, string sep, TextWriter textWriter)
+  {
+    Node? pointTo = node;
+
+    while (pointTo != null)
+    {
+      textWriter.Write(pointTo.data);
+
+      pointTo = pointTo.next;
+
+      if (pointTo != null)
+      {
+        textWriter.Write(sep);
+      }
+    }
+  }
+}