Fix reverse link when adding node to DoublyLinkedList. (TheAlgorithms#366)

Author: AngLv

DataStructures.Tests/LinkedList/DoublyLinkedListTests.cs

@@ -46,9 +46,11 @@ public static void TestAddtion()
             dll.Add(4);
 
             var arr = dll.GetData().ToArray();
+            var reversedArr = dll.GetDataReversed().ToArray();
 
             Assert.AreEqual(dll.Count, 5);
             Assert.AreEqual(new[] { 0, 1, 2, 3, 4 }, arr);
+            Assert.AreEqual(new[] { 4, 3, 2, 1, 0 }, reversedArr);
         }
 
         [Test]
@@ -61,9 +63,11 @@ public static void TestRemove()
             dll.Remove();
 
             var arr = dll.GetData().ToArray();
+            var reversedArr = dll.GetDataReversed().ToArray();
 
             Assert.AreEqual(dll.Count, 2);
             Assert.AreEqual(new[] { 1, 3 }, arr);
+            Assert.AreEqual(new[] { 3, 1 }, reversedArr);
         }
 
         [Test]

DataStructures/LinkedList/DoublyLinkedList/DoublyLinkedList.cs

@@ -113,9 +113,9 @@ public DoublyLinkedListNode<T> AddAfter(T data, DoublyLinkedListNode<T> existing
             node.Previous = existingNode;
             existingNode.Next = node;
 
-            if (existingNode.Next is not null)
+            if (node.Next is not null)
             {
-                existingNode.Next.Previous = node;
+                node.Next.Previous = node;
             }
 
             Count++;