/// <summary>
/// Reverse the order of the nodes of a doubly linked list in place, given the pointer to the head.
/// </summary>
/// <param name="head">pointer to the list head</param>
/// <returns>new list head</returns>
public static DblNode reverse(DblNode head)
{
DblNode previous = null;
DblNode current = head;
DblNode next = head.Next;
if (current == null || current.Next == null)
{
return(current);
} // empty or 1 node
while (current != null)
{
next = current.Next;
current.Next = previous;
current.Previous = current.Next;
previous = current;
current = next;
}
return(previous);
}
/// <summary>
/// Insert a node into a sorted double-linked list
/// </summary>
/// <param name="head"></param>
/// <param name="data"></param>
/// <returns></returns>
static DblNode SortedInsert(DblNode head, int data)
{
DblNode node = head;
DblNode newNode = new DblNode(data);
DblNode tempNode = head;
if (node == null)
{
return(new DblNode(data));
} // empty
// 1 node
if (node.Next == null)
{
if (head.Data < data)
{
head.Next = newNode;
newNode.Previous = head;
return(head);
}
else
{
newNode.Next = head;
head.Previous = newNode;
return(newNode);
}
}
// new data smaller or equal to head
if (head.Data >= data)
{
newNode.Next = head;
head.Previous = newNode;
return(newNode);
}
while (head != null)
{
if (head.Next == null)
{ // at the end of list
if (head.Data < data)
{
head.Next = newNode;
// head.prev.next = newNode;
newNode.Previous = head;
}
else
{
newNode.Previous = head.Previous;
newNode.Next = head;
head.Previous.Next = newNode;
head.Previous = newNode;
}
break;
}
else
{ // somewhere midway in the list
if (head.Next.Next != null)
{
if (data >= head.Data && data <= head.Next.Data)
{
newNode.Next = head.Next;
head.Next = newNode;
newNode.Previous = head;
break;
}
}
}
head = head.Next;
}
return(tempNode);
}