/// <summary>
/// Gets the previous node for a given node
/// </summary>
/// <param name="node"></param>
/// <returns></returns>
private NodeSingle GetPreviousNode(NodeSingle node)
{
var current = this._first;
while (current != null)
{
if (current.Next == node)
{
return(current);
}
current = current.Next;
}
return(null);
}
/// <summary>
/// Adds to the beginning of the Singularly Linked List
/// </summary>
/// <param name="item"></param>
public void AddFirst(int item)
{
var node = new NodeSingle(item);
if (this.IsEmpty())
{
this._first = this._last = node;
}
else
{
node.Next = this._first;
this._first = node;
}
this._size++;
}
private NodeSingle GetLastNode(NodeSingle head)
{
if (head == null)
{
throw new InvalidOperationException("No last available in an empty list");
}
var current = head;
while (current.Next != null)
{
current = current.Next;
}
return(current);
}
//Finding the middle element of the list for splitting
private NodeSingle GetMiddleNode(NodeSingle head)
{
if (head == null)
{
return(head);
}
NodeSingle slow = head, fast = head;
while (fast.Next != null && fast.Next.Next != null)
{
slow = slow.Next;
fast = fast.Next.Next;
}
return(slow);
}
//The main function
private NodeSingle MergeSort(NodeSingle head)
{
if (head == null || head.Next == null)
{
return(head);
}
//Get the middle of the list
var middle = this.GetMiddleNode(head);
//Split the list into two halfs
var leftHead = head;
var rightHead = middle.Next;
middle.Next = null;
return(this.Merge(this.MergeSort(leftHead), this.MergeSort(rightHead)));
}
//Merge subroutine to merge two sorted lists
private NodeSingle Merge(NodeSingle a, NodeSingle b)
{
NodeSingle dummyHead = new NodeSingle(-1);
NodeSingle current;
for (current = dummyHead; a != null && b != null; current = current.Next)
{
if (a.Value <= b.Value)
{
current.Next = a;
a = a.Next;
}
else
{
current.Next = b;
b = b.Next;
}
}
current.Next = (a == null) ? b : a;
return(dummyHead.Next);
}
/// <summary>
/// Reverses the LinkedList in place
/// </summary>
public void Reverse()
{
if (this.IsEmpty())
{
return;
}
var previous = this._first;
var current = this._first.Next;
while (current != null)
{
var next = current.Next;
current.Next = previous;
previous = current;
current = next;
}
this._last = this._first;
this._last.Next = null;
this._first = previous;
}
/// <summary>
/// Returns the last element in the list
/// </summary>
public int RemoveLast()
{
if (this.IsEmpty())
{
throw new InvalidOperationException("The list is empty");
}
var lastSaved = this._last.Value;
if (this._first == this._last)
{
this._first = this._last = null;
this._size--;
return(lastSaved);
}
var secondToLast = this.GetPreviousNode(this._last);
this._last = secondToLast;
this._last.Next = null;
this._size--;
return(lastSaved);
}
/// <summary>
/// Removes the first element in the list
/// </summary>
/// <param name="item"></param>
public int RemoveFirst()
{
if (this.IsEmpty())
{
throw new InvalidOperationException("The list is empty");
}
var firstSaved = this._first.Value;
if (this._first == this._last)
{
this._first = this._last = null;
this._size--;
return(firstSaved);
}
var second = this._first.Next;
this._first = null;
this._first = second;
this._size--;
return(firstSaved);
}
/// <summary>
/// Merge sort
/// </summary>
private void MergeSort()
{
this._first = this.MergeSort(this._first);
this._last = this.GetLastNode(this._first);
}
