Python Program to Reverse a Linked List using Recursion

This is a Python program to display the nodes of a linked list in reverse using recursion.

Problem Description

The program creates a linked list using data items input from the user and displays it in reverse.

Problem Solution

1. Create a class Node.
2. Create a class LinkedList.
3. Define methods append and display inside the class LinkedList to append data and display the linked list respectively.
4. Define methods display_reversed and display_reversed_helper.
5. display_reversed calls display_reversed_helper to display the list recursively in reverse.
6. Create an instance of LinkedList, append data to it and display the list in reverse order.

Program/Source Code

Here is the source code of a Python program to display the nodes of a linked list in reverse using recursion. The program output is shown below.

class Node:
    def __init__(self, data):
       self.data = data
       self.next = None
 
class LinkedList:
    def __init__(self):
        self.head = None
        self.last_node = None
 
    def append(self, data):
        if self.last_node is None:
            self.head = Node(data)
            self.last_node = self.head
        else:
            self.last_node.next = Node(data)
            self.last_node = self.last_node.next
 
    def display_reversed(self):
        self.display_reversed_helper(self.head)
 
    def display_reversed_helper(self, current):
        if current is None:
            return
 
        self.display_reversed_helper(current.next)
        print(current.data, end = ' ')
 
a_llist = LinkedList()
n = int(input('How many elements would you like to add? '))
for i in range(n):
    data = int(input('Enter data item: '))
    a_llist.append(data)
 
print('The reversed linked list: ', end = '')
a_llist.display_reversed()
Program Explanation

1. An instance of LinkedList is created.
2. The user is asked for the number of elements they would like to add. This is stored in n.
3. Using a loop, data from the user is appended to the linked list n times.
4. The linked list is displayed in reverse by calling the method display_reversed.

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Runtime Test Cases
Case 1:
How many elements would you like to add? 5
Enter data item: 3
Enter data item: 8
Enter data item: 14
Enter data item: 2
Enter data item: 1
The reversed linked list: 1 2 14 8 3 
 
Case 2:
How many elements would you like to add? 1
Enter data item: 3
The reversed linked list: 3 
 
Case 3:
How many elements would you like to add? 2
Enter data item: 0
Enter data item: 1
The reversed linked list: 1 0

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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