Improved code for DLList remove method.

Author: aubertc

source/code/projects/DLList_ICollection/DLList_ICollection/DLList.cs

@@ -41,7 +41,7 @@ public bool IsEmpty()
   // at the end of the list.
   public void Add(T value)
   {
-    if (isReadonly)
+    if (IsReadOnly)
     {
       throw new InvalidOperationException(
         "List is read-only."
@@ -108,7 +108,7 @@ public void CopyTo(T[] array, int arrayIndex)
 
   public bool Remove(T value)
   {
-    if (isReadonly)
+    if (IsReadOnly)
     {
       throw new InvalidOperationException(
         "List is read-only"
@@ -117,13 +117,26 @@ public bool Remove(T value)
     bool removed = false;
     if (!IsEmpty())
     {
+      // If the value we are looking for
+      // is held by head
       if (head.Data.Equals(value))
       {
         head = head.Next;
+        // If there was more than one
+        // cell in our list
         if (head != null)
         {
+          // We delete the reference
+          // to the node
+          // we want to remove.
           head.Previous = null;
         }
+        else
+        {
+          // Since there was only one cell in our list,
+          // the tail needs to be updated.
+          tail = null;
+        }
         removed = true;
       }
       else
@@ -133,13 +146,24 @@ public bool Remove(T value)
         {
           if (cCell.Next.Data.Equals(value))
           {
-            cCell.Next.Previous = cCell.Previous;
-
             cCell.Next = cCell.Next.Next;
+            // We test if we reached the end of the list
+            if (cCell.Next != null)
+            {
+              cCell.Next.Previous = cCell;
+            }
+            else
+            {
+              // If we did, we update the tail.
+              tail = cCell;
+            }
             removed = true;
           }
           else
           {
+            // If we did not find the value,
+            // we move the cCell to the next
+            // cell to continue searching.
             cCell = cCell.Next;
           }
         }
@@ -163,12 +187,7 @@ public int Count
     }
   }
 
-  public bool isReadonly = false;
-  public bool IsReadOnly
-  {
-    get { return isReadonly; }
-    set { isReadonly = value; }
-  }
+  public bool IsReadOnly { get; set; }
 
   public IEnumerator<T> GetEnumerator()
   {

source/code/projects/DLList_ICollection/DLList_ICollection/Program.cs

@@ -41,6 +41,10 @@ static void Main(string[] args)
     Console.WriteLine(myList1);
     Console.WriteLine("Removed 2: " + myList1.Remove(2));
     Console.WriteLine(myList1);
+    Console.WriteLine("Removed 1: " + myList1.Remove(1));
+    Console.WriteLine(myList1);
+    Console.WriteLine("Removed 22: " + myList1.Remove(22));
+    Console.WriteLine(myList1);
 
     // A benefit of realizing the ICollection interface
     // is that we can iterate over elements of lists now:
@@ -90,5 +94,59 @@ static void Main(string[] args)
     {
       Console.Write(i + " ");
     }
+    /*
+     * Testing Remove in detail
+     */
+
+    // Trying to remove from an empty list.
+    DLList<string> myList3 = new DLList<string>();
+    Console.WriteLine(myList3);
+    Console.WriteLine(
+      "Remove \"test\": " + myList3.Remove("Test")
+    );
+    Console.WriteLine(myList3);
+
+    // Trying to remove the only element of a list.
+    myList3.Add("Test");
+    Console.WriteLine(myList3);
+    Console.WriteLine(
+      "Remove \"test\": " + myList3.Remove("Test")
+    );
+    Console.WriteLine(myList3);
+
+    // Trying to remove the first element of a list of size 2.
+    myList3.Add("Test");
+    myList3.Add("String 1");
+    Console.WriteLine(myList3);
+    Console.WriteLine(
+      "Remove \"test\": " + myList3.Remove("Test")
+    );
+    Console.WriteLine(myList3);
+
+    // Trying to remove the last element of a list of size 3.
+    myList3.Add("String 2");
+    myList3.Add("Test");
+    Console.WriteLine(myList3);
+    Console.WriteLine(
+      "Remove \"test\": " + myList3.Remove("Test")
+    );
+    Console.WriteLine(myList3);
+
+    // Trying to remove an  element that is not in a list.
+    Console.WriteLine(myList3);
+    Console.WriteLine(
+      "Remove \"test\": " + myList3.Remove("Test")
+    );
+    Console.WriteLine(myList3);
+
+    // Trying to remove an element in the middle of a list of size 5.
+    myList3.Add("Test");
+    myList3.Add("String 3");
+    myList3.Add("String 4");
+    Console.WriteLine(myList3);
+    Console.WriteLine(
+      "Remove \"test\": " + myList3.Remove("Test")
+    );
+    Console.WriteLine(myList3);
   }
 }