**Reverse a doubly linked list**

### Problem Statement :

This challenge is part of a tutorial track by MyCodeSchool Given the pointer to the head node of a doubly linked list, reverse the order of the nodes in place. That is, change the next and prev pointers of the nodes so that the direction of the list is reversed. Return a reference to the head node of the reversed list. Note: The head node might be NULL to indicate that the list is empty. Function Description Complete the reverse function in the editor below. reverse has the following parameter(s): DoublyLinkedListNode head: a reference to the head of a DoublyLinkedList Returns - DoublyLinkedListNode: a reference to the head of the reversed list Input Format The first line contains an integer t, the number of test cases. Each test case is of the following format: The first line contains an integer n, the number of elements in the linked list. The next n lines contain an integer each denoting an element of the linked list.

### Solution :

` ````
Solution in C :
In C++ :
/*
Reverse a doubly linked list, input list may also be empty
Node is defined as
struct Node
{
int data;
Node *next;
Node *prev
}
*/
Node* Reverse(Node* head)
{
// Complete this function
// Do not write the main method.
Node *temp = NULL;
Node *current = head;
/* swap next and prev for all nodes of
doubly linked list */
while (current != NULL)
{
temp = current->prev;
current->prev = current->next;
current->next = temp;
current = current->prev;
}
/* Before changing head, check for the cases like empty
list and list with only one node */
if(temp != NULL )
head = temp->prev;
return head;
}
In Java :
/*
Insert Node at the end of a linked list
head pointer input could be NULL as well for empty list
Node is defined as
class Node {
int data;
Node next;
Node prev;
}
*/
Node Reverse(Node head) {
if(head==null)
return null;
if(head.next==null)
return head;
Node temp=head;
Node next=temp.next;
while(next!=null)
{
temp.next=temp.prev;
temp.prev=next;
temp=next;
next=next.next;
}
temp.next=temp.prev;
temp.prev=null;
return temp;
}
In python3 :
def Reverse(head):
if head == None or head.next == None:
return head
prev = head
curr = head.next
while curr.next != None:
prev, curr = curr, curr.next
head = curr
while prev != None:
curr.prev = curr.next
curr.next = prev
prev.next = prev.prev
prev.prev = curr
prev, curr = prev.next, prev
return head
In C :
// Complete the reverse function below.
/*
* For your reference:
*
* DoublyLinkedListNode {
* int data;
* DoublyLinkedListNode* next;
* DoublyLinkedListNode* prev;
* };
*
*/
DoublyLinkedListNode* reverse(DoublyLinkedListNode* head) {
struct DoublyLinkedListNode *prev,*curr,*next;
curr=head;
prev=NULL;
while(curr)
{
next=curr->next;
curr->next=prev;
curr->prev=next;
if(next==NULL)break;
prev=curr;curr=next;
}
curr->prev=NULL;return curr;
}
```

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