/// <summary>
///
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
public static DLNode Flatten(DLNode head)
{
DLNode curr = head;
while (curr != null)
{
DLNode endOfChild = null;
if (curr.child != null)
{
endOfChild = curr.child;
while (endOfChild.next != null)
{
endOfChild = endOfChild.next;
}
}
if (endOfChild != null)
{
DLNode next = curr.next;
curr.child.prev = curr;
curr.next = curr.child;
endOfChild.next = next;
if (next != null)
{
next.prev = endOfChild;
}
curr.child = null;
}
curr = curr.next;
}
return(head);
}
/** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
public void AddAtIndex(int index, int val)
{
if (index > lastNodeIndex + 1 || index < 0)
{
return;
}
if (index == lastNodeIndex + 1)
{
AddAtTail(val); return;
}
if (index == 0)
{
AddAtHead(val); return;
}
DLNode newNode = new DLNode(val);
DLNode curr = head;
DLNode prev = null;
while (index > 0)
{
prev = curr;
curr = curr.next;
index--;
}
newNode.prev = prev;
newNode.next = curr;
prev.next = newNode;
curr.prev = newNode;
lastNodeIndex++;
}
/** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
public int Get(int index)
{
if (index < 0 || index > lastNodeIndex)
{
return(-1);
}
DLNode curr = head;
while (index > 0 && curr != null)
{
curr = curr.next;
index--;
}
return(curr.val);
}
/** Append a node of value val to the last element of the linked list. */
public void AddAtTail(int val)
{
DLNode newNode = new DLNode(val);
newNode.next = null;
newNode.prev = last;
if (lastNodeIndex < 0)
{
AddAtHead(val);
return;
}
last.next = newNode;
last = newNode;
lastNodeIndex++;
}
/** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
public void AddAtHead(int val)
{
DLNode newNode = new DLNode(val);
newNode.prev = null;
newNode.next = head;
head = newNode;
lastNodeIndex++;
// if this is the first node added to the list then this will be last node as well.
if (lastNodeIndex == 0)
{
last = head;
}
else
{
head.prev = newNode;
}
}
/** Delete the index-th node in the linked list, if the index is valid. */
public void DeleteAtIndex(int index)
{
if (index < 0 || index > lastNodeIndex)
{
return;
}
DLNode curr = head;
DLNode prev = null;
while (index > 0)
{
prev = curr;
curr = curr.next;
index--;
}
if (curr == head)
{
head = head.next;
if (head != null)
{
// if there exists only 1 element and we removed the head
head.prev = null;
}
lastNodeIndex--;
return;
}
if (curr == last)
{
last = prev;
}
prev.next = curr.next;
if (curr.next != null)
{
// if last element is removed it won't have a prev to set
curr.next.prev = prev;
}
lastNodeIndex--;
}
/** Initialize your data structure here. */
public MyDoublyLinkedLink()
{
head = null;
last = null;
lastNodeIndex = -1;
}
