C++ Linked List Exercises: Reverse doubly linked list

C++ Linked List: Exercise-16 with Solution

Write a C++ program to create a doubly linked list of n nodes and display it in reverse order.

Test Data:
Doubly linked list is as follows:
Traversal in Forward direction:
Orange White Green Red
Traversal in Reverse direction:
Red Green White Orange
Reverse Doubly linked list:
Traversal in Forward direction:
Red Green White Orange
Traversal in Reverse direction:
Orange White Green Red

Sample Solution:

C++ Code:

 #include <iostream> // Including input-output stream header file

using namespace std; // Using standard namespace

// A doubly linked list node
struct Node {
   string data; // Data field to store string data
   struct Node* next; // Pointer to the next node
   struct Node* prev; // Pointer to the previous node
};

// Function to append data at the front of the doubly linked list
void append_data(Node** head, string new_data)
{
   // Create a new node and allocate memory.
   struct Node* newNode = new Node;

   // Assign data to the new node
   newNode->data = new_data;

   // A new node has been added with the name head and the previous node 
   // set to null, since it is being added at the front.
   newNode->next = (*head);
   newNode->prev = NULL;

   // Previous head is the new node
   if ((*head) != NULL)
   (*head)->prev = newNode;

   // Head points to new node
   (*head) = newNode;
}

// Function to reverse a doubly linked list
void reverse(Node** head)
{
    struct Node* tmp = NULL; // Temporary node for swapping
    struct Node* currNode = *head; // Current node to traverse the list

    while (currNode != NULL) {
        // Swap this node’s next and prev references
        tmp = currNode->prev;
        currNode->prev = currNode->next;
        currNode->next = tmp;
        // The next node is now the prev node because of the swap
        currNode = currNode->prev;
    }
    // If tmp is not NULL, then head needs to be updated
    if (tmp != NULL)
        *head = tmp->prev;
}

// Function to display contents of the doubly linked list
void displayDlList(Node* head)
{
    Node* last_node;
    cout << "\n\nTraversal in Forward direction:\n";
    while (head != NULL) {
        cout << " " << head->data << " "; // Displaying data in forward direction
        last_node = head;
        head = head->next;
    }
    cout << "\nTraversal in Reverse direction:\n";
    while (last_node != NULL) {
        cout << " " << last_node->data << " "; // Displaying data in reverse direction
        last_node = last_node->prev;
    }
}

// Main program
int main() {
   /* Start with the empty list */
   struct Node* head = NULL; // Initializing the head of the linked list as NULL
   append_data(&head, "Red"); // Appending "Red" at the front of the list
   append_data(&head, "Green"); // Appending "Green" at the front of the list
   append_data(&head, "White"); // Appending "White" at the front of the list
   append_data(&head, "Orange"); // Appending "Orange" at the front of the list  
   cout<<"Doubly linked list is as follows: ";
   displayDlList(head); // Displaying the doubly linked list
   reverse(&head); // Reversing the doubly linked list
   cout<<"\n\nReverse Doubly linked list: ";
   displayDlList(head); // Displaying the reversed doubly linked list
   return 0; // Returning from the main function
}

Sample Output:

Doubly linked list is as follows:

Traversal in Forward direction:
 Orange  White  Green  Red
Traversal in Reverse direction:
 Red  Green  White  Orange

Reverse Doubly linked list:

Traversal in Forward direction:
 Red  Green  White  Orange
Traversal in Reverse direction:
 Orange  White  Green  Red

Flowchart:

CPP Code Editor:

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