**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 :
// 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
```

## View More Similar Problems

## Tree: Postorder Traversal

Complete the postorder function in the editor below. It received 1 parameter: a pointer to the root of a binary tree. It must print the values in the tree's postorder traversal as a single line of space-separated values. Input Format Our test code passes the root node of a binary tree to the postorder function. Constraints 1 <= Nodes in the tree <= 500 Output Format Print the

View Solution →## Tree: Inorder Traversal

In this challenge, you are required to implement inorder traversal of a tree. Complete the inorder function in your editor below, which has 1 parameter: a pointer to the root of a binary tree. It must print the values in the tree's inorder traversal as a single line of space-separated values. Input Format Our hidden tester code passes the root node of a binary tree to your $inOrder* func

View Solution →## Tree: Height of a Binary Tree

The height of a binary tree is the number of edges between the tree's root and its furthest leaf. For example, the following binary tree is of height : image Function Description Complete the getHeight or height function in the editor. It must return the height of a binary tree as an integer. getHeight or height has the following parameter(s): root: a reference to the root of a binary

View Solution →## Tree : Top View

Given a pointer to the root of a binary tree, print the top view of the binary tree. The tree as seen from the top the nodes, is called the top view of the tree. For example : 1 \ 2 \ 5 / \ 3 6 \ 4 Top View : 1 -> 2 -> 5 -> 6 Complete the function topView and print the resulting values on a single line separated by space.

View Solution →## Tree: Level Order Traversal

Given a pointer to the root of a binary tree, you need to print the level order traversal of this tree. In level-order traversal, nodes are visited level by level from left to right. Complete the function levelOrder and print the values in a single line separated by a space. For example: 1 \ 2 \ 5 / \ 3 6 \ 4 F

View Solution →## Binary Search Tree : Insertion

You are given a pointer to the root of a binary search tree and values to be inserted into the tree. Insert the values into their appropriate position in the binary search tree and return the root of the updated binary tree. You just have to complete the function. Input Format You are given a function, Node * insert (Node * root ,int data) { } Constraints No. of nodes in the tree <

View Solution →