/// <summary>
/// Merges two ordered sublists
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="aNode">Left part of sublist</param>
/// <param name="bNode">Right part of sublist</param>
/// <param name="tailNode">Tail node of the merged list</param>
/// <returns>The result of merging</returns>
private static DataStructures.Linear.LinkedListNode <T> Merge <T>(DataStructures.Linear.LinkedListNode <T> leftNode,
DataStructures.Linear.LinkedListNode <T> rightNode,
ref DataStructures.Linear.LinkedListNode <T> tailNode) where T : IComparable <T>
{
var dummyHead = new DataStructures.Linear.LinkedListNode <T>();
var curNode = dummyHead;
while (leftNode != null || rightNode != null)
{
if (rightNode == null)
{
curNode.Next = leftNode;
leftNode = leftNode.Next;
}
else if (leftNode == null)
{
curNode.Next = rightNode;
rightNode = rightNode.Next;
}
else if (leftNode.Value.CompareTo(rightNode.Value) <= 0)
{
curNode.Next = leftNode;
leftNode = leftNode.Next;
}
else
{
curNode.Next = rightNode;
rightNode = rightNode.Next;
}
curNode = curNode.Next;
}
tailNode = curNode;
return(dummyHead.Next);
}
/// <summary>
/// Returns the sentinel node
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="firstNode"></param>
/// <returns></returns>
private static DataStructures.Linear.LinkedListNode <T> GetSentinelNode <T>(DataStructures.Linear.LinkedListNode <T> firstNode) where T : IComparable <T>
{
var curNode = firstNode;
while (curNode != null && curNode.Next != null && curNode.Value.CompareTo(curNode.Next.Value) <= 0)
{
curNode = curNode.Next;
}
return(curNode);
}
private static DataStructures.Linear.LinkedListNode <T> GetMiddle <T>(DataStructures.Linear.LinkedListNode <T> firstNode) where T : IComparable <T>
{
if (firstNode.Next == null)
{
return(firstNode);
}
DataStructures.Linear.LinkedListNode <T> fast, slow;
fast = slow = firstNode;
while (fast.Next != null && fast.Next.Next != null)
{
slow = slow.Next;
fast = fast.Next.Next;
}
return(slow);
}
private static DataStructures.Linear.LinkedListNode <T> ShuffledMerge <T>(DataStructures.Linear.LinkedListNode <T> leftNode, DataStructures.Linear.LinkedListNode <T> rightNode) where T : IComparable <T>
{
var dummyHead = new DataStructures.Linear.LinkedListNode <T>();
DataStructures.Linear.LinkedListNode <T> curNode = dummyHead;
var rnd = new Random((int)DateTime.Now.Ticks);
while (leftNode != null || rightNode != null)
{
var rndRes = rnd.Next(0, 2);
if (rndRes == 0)
{
if (leftNode != null)
{
curNode.Next = leftNode;
leftNode = leftNode.Next;
}
else
{
curNode.Next = rightNode;
rightNode = rightNode.Next;
}
}
else
{
if (rightNode != null)
{
curNode.Next = rightNode;
rightNode = rightNode.Next;
}
else
{
curNode.Next = leftNode;
leftNode = leftNode.Next;
}
}
curNode = curNode.Next;
}
return(dummyHead.Next);
}
public static DataStructures.Linear.LinkedListNode <T> Shuffle <T>(DataStructures.Linear.LinkedListNode <T> firstNode) where T : IComparable <T>
{
if (firstNode == null)
{
throw new ArgumentNullException(nameof(firstNode));
}
if (firstNode.Next == null)
{
return(firstNode);
}
var middle = GetMiddle(firstNode);
var rightNode = middle.Next;
middle.Next = null;
var mergedResult = ShuffledMerge(Shuffle(firstNode), Shuffle(rightNode));
return(mergedResult);
}
public static DataStructures.Linear.LinkedListNode <T> Sort <T>(DataStructures.Linear.LinkedListNode <T> firstNode) where T : IComparable <T>
{
if (firstNode is null)
{
throw new ArgumentNullException(nameof(firstNode));
}
if (firstNode.Next == null)
{
return(firstNode);
}
var head = firstNode;
var leftNode = head;
var iterNum = 0;
while (leftNode != null)
{
//Let's start again from the beginning
leftNode = head;
iterNum = 0;
DataStructures.Linear.LinkedListNode <T> tailNode = null;
while (leftNode != null)
{
//Let's get the left sublist
//Let's find the node which divides sublist into two ordered sublists
var sentinelNode = GetSentinelNode(leftNode);
var rightNode = sentinelNode.Next;
//If the right node is null it means that we don't have two sublist and the left sublist is ordered already
//so we just add the rest sublist to the tail
if (rightNode == null)
{
if (tailNode == null)
{
break;
}
tailNode.Next = leftNode;
break;
}
sentinelNode.Next = null;
//Let's find the node where the right sublist ends
sentinelNode = GetSentinelNode(rightNode);
var restNode = sentinelNode.Next;
sentinelNode.Next = null;
DataStructures.Linear.LinkedListNode <T> newTailNode = null;
//Merging of two ordered sublists
var mergedList = Merge(leftNode, rightNode, ref newTailNode);
//If we're at the beginning of the list the head of the merged sublist becomes the head of the list
if (iterNum == 0)
{
head = mergedList;
}
else //add the
{
tailNode.Next = mergedList;
}
tailNode = newTailNode;
leftNode = restNode;
iterNum++;
}
if (iterNum == 0)
{
break;
}
}
return(head);
}
