Reverse a doubly linked list

                            Solution in C :

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;

}
                        

                        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;
}
                    

                        Solution in Java :

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;

}
                    

                        Solution in Python : 
                            
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