使用递归反转双向链表

给定一个双向链表。使用递归将其反转。

Original Doubly linked list 

Reversed Doubly linked list 

我们已经讨论过
逆向双向链接列表的迭代解决方案

算法
1)如果列表为空，则返回
2)通过交换head-> prev和head-> next来反转头部
3)如果prev = NULL，则表示列表已完全反转。否则反转(head-> prev)

C++

// C++ implementation to reverse a doubly
// linked list using recursion
#include 
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 = new Node;
    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
Node* Reverse(Node* node)
{
    // If empty list, return
    if (!node)
        return NULL;
  
    // Otherwise, swap the next and prev
    Node* temp = node->next;
    node->next = node->prev;
    node->prev = temp;
  
    // If the prev is now NULL, the list
    // has been fully reversed
    if (!node->prev)
        return node;
  
    // Otherwise, keep going
    return Reverse(node->prev);
}
  
// 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
    head = Reverse(head);
    cout << "\nReversed list: ";
    printList(head);
    return 0;
}

Java

// Java implementation to reverse a doubly 
// linked list using recursion 
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(); 
    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 Reverse(Node node) 
{ 
    // If empty list, return 
    if (node == null) 
        return null; 
  
    // Otherwise, swap the next and prev 
    Node temp = node.next; 
    node.next = node.prev; 
    node.prev = temp; 
  
    // If the prev is now null, the list 
    // has been fully reversed 
    if (node.prev == null) 
        return node; 
  
    // Otherwise, keep going 
    return Reverse(node.prev); 
} 
  
// 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 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)); 
    System.out.print( "Original list: "); 
    printList(head); 
  
    // Reverse doubly linked list 
    head = Reverse(head); 
    System.out.print("\nReversed list: "); 
    printList(head); 
} 
}
  
// This code is contributed by Arnab Kundu

Python3

# Python3 implementation to reverse a doubly
# linked list using recursion
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)
    new_node.data = data
    new_node.next = 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 Reverse(node):
      
    # If empty list, return
    if not node:
        return None
  
    # Otherwise, swap the next and prev
    temp = node.next
    node.next = node.prev
    node.prev = temp
  
    # If the prev is now None, the list
    # has been fully reversed
    if not node.prev:
        return node
  
    # Otherwise, keep going
    return Reverse(node.prev)
  
# 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 = Reverse(head)
    print("\nReversed list: ", end = "")
    printList(head)
      
# This code is contributed by Srathore

C#

// C# implementation to reverse a doubly 
using System;
  
// linked list using recursion 
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(); 
    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 Reverse(Node node) 
{ 
    // If empty list, return 
    if (node == null) 
        return null; 
  
    // Otherwise, swap the next and prev 
    Node temp = node.next; 
    node.next = node.prev; 
    node.prev = temp; 
  
    // If the prev is now null, the list 
    // has been fully reversed 
    if (node.prev == null) 
        return node; 
  
    // Otherwise, keep going 
    return Reverse(node.prev); 
} 
  
// 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 []argsS) 
{ 
    // 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 = Reverse(head); 
    Console.Write("\nReversed list: "); 
    printList(head); 
} 
} 
  
// This code is contributed by Arnab Kundu

输出：

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