Invertir una lista doblemente enlazada | Conjunto-2 – Part 1

Escriba un programa para invertir la lista doblemente enlazada dada.

Vea los diagramas a continuación, por ejemplo.

          (a) Original Doubly Linked List  

          (b) Reversed Doubly Linked List  

Enfoque: en la publicación anterior , la lista doblemente vinculada se invierte intercambiando los punteros anterior y siguiente para todos los Nodes, cambiando la anterior del encabezado (o inicio) y luego cambiando el puntero del encabezado al final. En esta publicación, creamos una función push que agrega el Node dado al comienzo de la lista dada. Recorremos la lista original y, uno por uno, pasamos el puntero del Node actual a la función push. Este proceso invertirá la lista. Finalmente devuelva el nuevo encabezado de esta lista invertida.

// C++ implementation to reverse
// a doubly linked list
#include <bits/stdc++.h>
 
using namespace std;
 
// a node of the doubly linked list
struct Node {
    int data;
    Node *next, *prev;
};
 
// function to get a new node
Node* getNode(int data)
{
    // allocate space
    Node* new_node = (Node*)malloc(sizeof(Node));
 
    // put in the data
    new_node->data = data;
    new_node->next = new_node->prev = NULL;
    return new_node;
}
 
// function to insert a node at the beginning
// of the Doubly Linked List
void push(Node** head_ref, Node* new_node)
{
    // since we are adding at the beginning,
    // prev is always NULL
    new_node->prev = NULL;
 
    // link the old list off the new node
    new_node->next = (*head_ref);
 
    // change prev of head node to new node
    if ((*head_ref) != NULL)
        (*head_ref)->prev = new_node;
 
    // move the head to point to the new node
    (*head_ref) = new_node;
}
 
// function to reverse a doubly linked list
void reverseList(Node** head_ref)
{
    // if list is empty or it contains
    // a single node only
    if (!(*head_ref) || !((*head_ref)->next))
        return;
 
    Node* new_head = NULL;
    Node *curr = *head_ref, *next;
 
    while (curr != NULL) {
 
        // get pointer to next node
        next = curr->next;
 
        // push 'curr' node at the beginning of the
        // list with starting with 'new_head'
        push(&new_head, curr);
 
        // update 'curr'
        curr = next;
    }
 
    // update 'head_ref'
    *head_ref = new_head;
}
 
// Function to print nodes in a
// given doubly linked list
void printList(Node* head)
{
    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
}
 
// Driver program to test above
int main()
{
    // Start with the empty list
    Node* head = NULL;
 
    // Create doubly linked: 10<->8<->4<->2 */
    push(&head, getNode(2));
    push(&head, getNode(4));
    push(&head, getNode(8));
    push(&head, getNode(10));
 
    cout << "Original list: ";
    printList(head);
 
    // Reverse doubly linked list
    reverseList(&head);
 
    cout << "\nReversed list: ";
    printList(head);
 
    return 0;
}

// Java implementation to reverse
// a doubly linked list
class GFG
{
 
// a node of the doubly linked list
static class Node
{
    int data;
    Node next, prev;
};
 
// function to get a new node
static Node getNode(int data)
{
    // allocate space
    Node new_node = new Node();
 
    // put in the data
    new_node.data = data;
    new_node.next = new_node.prev = null;
    return new_node;
}
 
// function to insert a node at the beginning
// of the Doubly Linked List
static Node push(Node head_ref, Node new_node)
{
    // since we are adding at the beginning,
    // prev is always null
    new_node.prev = null;
 
    // link the old list off the new node
    new_node.next = (head_ref);
 
    // change prev of head node to new node
    if ((head_ref) != null)
        (head_ref).prev = new_node;
 
    // move the head to point to the new node
    (head_ref) = new_node;
     
    return head_ref;
}
 
// function to reverse a doubly linked list
static Node reverseList(Node head_ref)
{
    // if list is empty or it contains
    // a single node only
    if ((head_ref) == null || ((head_ref).next) == null)
        return null;
 
    Node new_head = null;
    Node curr = head_ref, next;
 
    while (curr != null)
    {
 
        // get pointer to next node
        next = curr.next;
 
        // push 'curr' node at the beginning of the
        // list with starting with 'new_head'
        new_head = push(new_head, curr);
 
        // update 'curr'
        curr = next;
    }
 
    // update 'head_ref'
    head_ref = new_head;
     
    return head_ref;
}
 
// Function to print nodes in a
// given doubly linked list
static void printList(Node head)
{
    while (head != null)
    {
        System.out.print(head.data + " ");
        head = head.next;
    }
}
 
// Driver program to test above
public static void main(String args[])
{
    // Start with the empty list
    Node head = null;
 
    // Create doubly linked: 10< - >8< - >4< - >2 /
    head = push(head, getNode(2));
    head = push(head, getNode(4));
    head = push(head, getNode(8));
    head = push(head, getNode(10));
 
    System.out.print("Original list: ");
    printList(head);
 
    // Reverse doubly linked list
    head = reverseList(head);
 
    System.out.print("\nReversed list: ");
    printList(head);
}
}
 
// This code is contributed by Arnab Kundu

# Python3 implementation to reverse
# a doubly linked list
import math
 
# a node of the doubly linked list
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# function to get a new node
def getNode(data):
     
    # allocate space
    new_node = Node(data)
 
    # put in the data
    new_node.data = data
    new_node.next = None
    new_node.prev = None
    return new_node
 
# function to insert a node at the beginning
# of the Doubly Linked List
def push(head_ref, new_node):
     
    # since we are adding at the beginning,
    # prev is always None
    new_node.prev = None
 
    # link the old list off the new node
    new_node.next = head_ref
 
    # change prev of head node to new node
    if (head_ref != None):
        head_ref.prev = new_node
 
    # move the head to point to the new node
    head_ref = new_node
    return head_ref
 
# function to reverse a doubly linked list
def reverseList(head_ref):
     
    # if list is empty or it contains
    # a single node only
    if (head_ref == None or
       (head_ref).next == None):
        return None
 
    new_head = None
    curr = head_ref
 
    while (curr != None):
 
        # get pointer to next node
        next = curr.next
 
        # push 'curr' node at the beginning of the
        # list with starting with 'new_head'
        new_head = push(new_head, curr)
 
        # update 'curr'
        curr = next
     
    # update 'head_ref'
    head_ref = new_head
 
    return head_ref
 
# Function to print  nodes in a
# given doubly linked list
def printList(head):
    while (head != None) :
        print(head.data, end = " ")
        head = head.next
 
# Driver Code
if __name__=='__main__':
     
    # Start with the empty list
    head = None
 
    # Create doubly linked: 10<.8<.4<.2 */
    head = push(head, getNode(2));
    head = push(head, getNode(4));
    head = push(head, getNode(8));
    head = push(head, getNode(10));
 
    print("Original list: ", end = "")
    printList(head)
 
    # Reverse doubly linked list
    head = reverseList(head)
 
    print("\nReversed list: ", end = "")
    printList(head)
 
# This code is contributed by Srathore

// C# implementation to reverse
// a doubly linked list
using System;
 
class GFG
{
 
// a node of the doubly linked list
public class Node
{
    public int data;
    public Node next, prev;
};
 
// function to get a new node
static Node getNode(int data)
{
    // allocate space
    Node new_node = new Node();
 
    // put in the data
    new_node.data = data;
    new_node.next = new_node.prev = null;
    return new_node;
}
 
// function to insert a node at the beginning
// of the Doubly Linked List
static Node push(Node head_ref, Node new_node)
{
    // since we are adding at the beginning,
    // prev is always null
    new_node.prev = null;
 
    // link the old list off the new node
    new_node.next = (head_ref);
 
    // change prev of head node to new node
    if ((head_ref) != null)
        (head_ref).prev = new_node;
 
    // move the head to point to the new node
    (head_ref) = new_node;
     
    return head_ref;
}
 
// function to reverse a doubly linked list
static Node reverseList(Node head_ref)
{
    // if list is empty or it contains
    // a single node only
    if ((head_ref) == null || ((head_ref).next) == null)
        return null;
 
    Node new_head = null;
    Node curr = head_ref, next;
 
    while (curr != null)
    {
 
        // get pointer to next node
        next = curr.next;
 
        // push 'curr' node at the beginning of the
        // list with starting with 'new_head'
        new_head = push(new_head, curr);
 
        // update 'curr'
        curr = next;
    }
 
    // update 'head_ref'
    head_ref = new_head;
     
    return head_ref;
}
 
// Function to print nodes in a
// given doubly linked list
static void printList(Node head)
{
    while (head != null)
    {
        Console.Write(head.data + " ");
        head = head.next;
    }
}
 
// Driver code
public static void Main(String []args)
{
    // Start with the empty list
    Node head = null;
 
    // Create doubly linked: 10< - >8< - >4< - >2 /
    head = push(head, getNode(2));
    head = push(head, getNode(4));
    head = push(head, getNode(8));
    head = push(head, getNode(10));
 
    Console.Write("Original list: ");
    printList(head);
 
    // Reverse doubly linked list
    head = reverseList(head);
 
    Console.Write("\nReversed list: ");
    printList(head);
}
}
 
// This code has been contributed by 29AjayKumar

<script>
// javascript implementation to reverse
// a doubly linked list     // a node of the doubly linked list
class Node {
    constructor() {
        this.data = 0;
        this.prev = null;
        this.next = null;
    }
}
    // function to get a new node
    function getNode(data) {
        // allocate space
var new_node = new Node();
 
        // put in the data
        new_node.data = data;
        new_node.next = new_node.prev = null;
        return new_node;
    }
 
    // function to insert a node at the beginning
    // of the Doubly Linked List
    function push(head_ref,  new_node) {
        // since we are adding at the beginning,
        // prev is always null
        new_node.prev = null;
 
        // link the old list off the new node
        new_node.next = (head_ref);
 
        // change prev of head node to new node
        if ((head_ref) != null)
            (head_ref).prev = new_node;
 
        // move the head to point to the new node
        (head_ref) = new_node;
 
        return head_ref;
    }
 
    // function to reverse a doubly linked list
    function reverseList(head_ref) {
        // if list is empty or it contains
        // a single node only
        if ((head_ref) == null || ((head_ref).next) == null)
            return null;
 
var new_head = null;
var curr = head_ref, next;
 
        while (curr != null) {
 
            // get pointer to next node
            next = curr.next;
 
            // push 'curr' node at the beginning of the
            // list with starting with 'new_head'
            new_head = push(new_head, curr);
 
            // update 'curr'
            curr = next;
        }
 
        // update 'head_ref'
        head_ref = new_head;
 
        return head_ref;
    }
 
    // Function to print nodes in a
    // given doubly linked list
    function printList(head) {
        while (head != null) {
            document.write(head.data + " ");
            head = head.next;
        }
    }
 
    // Driver program to test above
     
        // Start with the empty list
var head = null;
 
        // Create doubly linked: 10< - >8< - >4< - >2 /
        head = push(head, getNode(2));
        head = push(head, getNode(4));
        head = push(head, getNode(8));
        head = push(head, getNode(10));
 
        document.write("Original list: ");
        printList(head);
 
        // Reverse doubly linked list
        head = reverseList(head);
 
        document.write("<br/>Reversed list: ");
        printList(head);
 
// This code contributed by Rajput-Ji
</script>

Producción: 

Original list: 10 8 4 2
Reversed list: 2 4 8 10

Complejidad temporal: O(n).