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
- 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) {
        return null;
        return head;
    Node temp=head;
    return temp;


In python3 :

def Reverse(head):
	if head == None or == None:
		return head

	prev = head
	curr =

	while != None:
		prev, curr = curr,

	head = curr

	while prev != None:
		curr.prev = = prev = prev.prev
		prev.prev = curr
		prev, curr =, 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->prev=NULL;return curr;


View More Similar Problems

Equal Stacks

ou have three stacks of cylinders where each cylinder has the same diameter, but they may vary in height. You can change the height of a stack by removing and discarding its topmost cylinder any number of times. Find the maximum possible height of the stacks such that all of the stacks are exactly the same height. This means you must remove zero or more cylinders from the top of zero or more of

View Solution →

Game of Two Stacks

Alexa has two stacks of non-negative integers, stack A = [a0, a1, . . . , an-1 ] and stack B = [b0, b1, . . . , b m-1] where index 0 denotes the top of the stack. Alexa challenges Nick to play the following game: In each move, Nick can remove one integer from the top of either stack A or stack B. Nick keeps a running sum of the integers he removes from the two stacks. Nick is disqualified f

View Solution →

Largest Rectangle

Skyline Real Estate Developers is planning to demolish a number of old, unoccupied buildings and construct a shopping mall in their place. Your task is to find the largest solid area in which the mall can be constructed. There are a number of buildings in a certain two-dimensional landscape. Each building has a height, given by . If you join adjacent buildings, they will form a solid rectangle

View Solution →

Simple Text Editor

In this challenge, you must implement a simple text editor. Initially, your editor contains an empty string, S. You must perform Q operations of the following 4 types: 1. append(W) - Append W string to the end of S. 2 . delete( k ) - Delete the last k characters of S. 3 .print( k ) - Print the kth character of S. 4 . undo( ) - Undo the last (not previously undone) operation of type 1 or 2,

View Solution →

Poisonous Plants

There are a number of plants in a garden. Each of the plants has been treated with some amount of pesticide. After each day, if any plant has more pesticide than the plant on its left, being weaker than the left one, it dies. You are given the initial values of the pesticide in each of the plants. Determine the number of days after which no plant dies, i.e. the time after which there is no plan

View Solution →

AND xor OR

Given an array of distinct elements. Let and be the smallest and the next smallest element in the interval where . . where , are the bitwise operators , and respectively. Your task is to find the maximum possible value of . Input Format First line contains integer N. Second line contains N integers, representing elements of the array A[] . Output Format Print the value

View Solution →