/// <summary>
/// Replaces the Head of the list with the new value.
/// </summary>
/// <param name="data"> Value for the new Head of the list.</param>
/// <returns>The new Head node.</returns>
public DoublyLinkedListNode <T> AddHead(T data)
{
var node = new DoublyLinkedListNode <T>(data);
if (Head is null)
{
Head = node;
Tail = node;
Count = 1;
return(node);
}
Head.Previous = node;
node.Next = Head;
Head = node;
Count++;
return(node);
}
/// <summary>
/// Removes the last node in the list.
/// </summary>
public void Remove()
{
if (Tail is null)
{
throw new InvalidOperationException("Cannot prune empty list");
}
Tail = Tail.Previous;
if (Tail is null)
{
Head = null;
Count = 0;
return;
}
Tail.Next = null;
Count--;
}
/// <summary>
/// Removes the Head and replaces it with the second node in the list.
/// </summary>
public void RemoveHead()
{
if (Head is null)
{
throw new InvalidOperationException();
}
Head = Head.Next;
if (Head is null)
{
Tail = null;
Count = 0;
return;
}
Head.Previous = null;
Count--;
}
/// <summary>
/// Removes the first item in the list
/// </summary>
public void RemoveFirst()
{
if (Count != 0)
{
// Remove the head node
_head = _head.Next;
// Decrement the count
Count--;
if (Count == 0)
{
// List is now empty, null the tail
_tail = null;
}
else
{
// null the heads previous property
_head.Previous = null;
}
}
}
/// <summary>
/// Reverses the list. Because of how doubly linked list are structured this is not a complex action.
/// </summary>
public void Reverse()
{
DoublyLinkedListNode <T>?current = Head;
DoublyLinkedListNode <T>?temp = null;
while (current != null)
{
temp = current.Previous;
current.Previous = current.Next;
current.Next = temp;
current = current.Previous;
}
Tail = Head;
// temp can be null on empty list
if (temp != null)
{
Head = temp.Previous;
}
}
/// <summary>
/// Adds a new value after an existing node.
/// </summary>
/// <param name="data"> New value to be added to the list.</param>
/// <param name="existingNode"> An existing node in the list.</param>
/// <returns>The new node created based on the new value.</returns>
public DoublyLinkedListNode <T> AddAfter(T data, DoublyLinkedListNode <T> existingNode)
{
if (existingNode == Tail)
{
return(Add(data));
}
var node = new DoublyLinkedListNode <T>(data);
node.Next = existingNode.Next;
node.Previous = existingNode;
existingNode.Next = node;
if (existingNode.Next != null)
{
existingNode.Next.Previous = node;
}
Count++;
return(node);
}
/// <summary>
/// Remove the first occurance of an element from the list.
/// </summary>
/// <param name="item"></param>
/// <returns></returns>
public bool Remove(T item)
{
DoublyLinkedListNode <T> previous = null;
DoublyLinkedListNode <T> current = Head;
while (current != null)
{
if (current.Value.Equals(item))
{
// A node in the middle or end
if (previous != null)
{
previous.Next = current.Next;
if (current.Next == null)
{
Tail = previous;
}
else
{
current.Next.Previous = previous;
}
Count--;
}
else
{
RemoveFirst();
}
return(true);
}
previous = current;
current = current.Next;
}
return(false);
}
public void RemoveLast()
{
if (Count != 0)
{
if (Count == 1)
{
// Removing only node in list
// null the head and tail
_head = null;
_tail = null;
}
else
{
// Set the preceding node as the tail
_tail = _tail.Previous;
// Set the tail's Next property to null
_tail.Next = null;
}
// Decrement the count
Count--;
}
}
/// <summary>
/// Removes specific node.
/// </summary>
/// <param name="node"> Node to be removed.</param>
public void RemoveNode(DoublyLinkedListNode <T> node)
{
if (node == Head)
{
RemoveHead();
return;
}
if (node == Tail)
{
Remove();
return;
}
if (node.Previous is null || node.Next is null)
{
throw new ArgumentException($"{nameof(node)} cannot have Previous or Next null if it's an internal node");
}
node.Previous.Next = node.Next;
node.Next.Previous = node.Previous;
Count--;
}
/// <summary>
/// Adds an item to the end of the list
/// </summary>
/// <param name="item">The item to add to the end of the list</param>
public void AddLast(T item)
{
// Create a new node
DoublyLinkedListNode <T> node = new DoublyLinkedListNode <T>(item);
if (Count == 0)
{
// The list is empty, the new node will be head and the tail
_head = node;
}
else
{
// Set the current tails Next property to the new node
_tail.Next = node;
// Set the nodes Previous property to the current tail
node.Previous = _tail;
}
// Make the new node the tail
_tail = node;
// Increment the Count
Count++;
}
/// <summary>
/// Removes all items from the list
/// </summary>
public void Clear()
{
_head = null;
_tail = null;
Count = 0;
}
/// <summary>
/// Initializes a new instance of the <see cref="DoublyLinkedList{T}"/> class.
/// </summary>
/// <param name="data"> Data of the original head of the list.</param>
public DoublyLinkedList(T data)
{
Head = new DoublyLinkedListNode <T>(data);
Tail = Head;
Count = 1;
}