// link - https://www.hackerrank.com/challenges/reverse-a-doubly-linked-list/problem?h_l=interview&playlist_slugs%5B%5D=interview-preparation-kit&playlist_slugs%5B%5D=linked-lists
private static void Main(string[] args)
{
int t = Convert.ToInt32(Console.ReadLine());
for (int tItr = 0; tItr < t; tItr++)
{
DoublyLinkedList llist = new DoublyLinkedList();
int llistCount = Convert.ToInt32(Console.ReadLine());
for (int i = 0; i < llistCount; i++)
{
int llistItem = Convert.ToInt32(Console.ReadLine());
llist.InsertNode(llistItem);
}
DoublyLinkedListNode llist1 = reverse(llist.head);
PrintDoublyLinkedList(llist1, " ");
}
}
private static DoublyLinkedListNode reverse(DoublyLinkedListNode head)
{
if (head == null || head.next == null)
{
return(head);
}
// ONLINE SOLUTION WITHOUT USING EXTRA SPACE
var cur = head;
var prev = head.prev;
while (cur != null)
{
var next = cur.next;
cur.next = prev;
prev = cur;
cur = next;
}
return(prev);
// MY SOLUTION - NEW LINKED LIST
//var newDLL = new DoublyLinkedList();
//// get last node
//var cur = head;
//while (cur.next != null)
// cur = cur.next;
//while (cur != null)
//{
// newDLL.InsertNode(cur.data);
// cur = cur.prev;
//}
//return newDLL.head;
}
public DoublyLinkedListNode(int nodeData)
{
this.data = nodeData;
this.next = null;
this.prev = null;
}
public DoublyLinkedList()
{
this.head = null;
this.tail = null;
}
