Python Program to Reverse a linked list

Last Updated : 10 Jan, 2023

Given pointer to the head node of a linked list, the task is to reverse the linked list. We need to reverse the list by changing links between nodes.

Examples:

Input : Head of following linked list  
       1->2->3->4->NULL
Output : Linked list should be changed to,
       4->3->2->1->NULL

Input : Head of following linked list  
       1->2->3->4->5->NULL
Output : Linked list should be changed to,
       5->4->3->2->1->NULL

Input : NULL
Output : NULL

Input  : 1->NULL
Output : 1->NULL

Iterative Method

Python3

# Python program to reverse a linked list 
# Time Complexity : O(n) 
# Space Complexity : O(n) as 'next'  
#variable is getting created in each loop. 
  
# Node class 
  
  
class Node: 
  
    # Constructor to initialize the node object 
    def __init__(self, data): 
        self.data = data 
        self.next = None
  
  
class LinkedList: 
  
    # Function to initialize head 
    def __init__(self): 
        self.head = None
  
    # Function to reverse the linked list 
    def reverse(self): 
        prev = None
        current = self.head 
        while(current is not None): 
            next = current.next
            current.next = prev 
            prev = current 
            current = next
        self.head = prev 
  
    # Function to insert a new node at the beginning 
    def push(self, new_data): 
        new_node = Node(new_data) 
        new_node.next = self.head 
        self.head = new_node 
  
    # Utility function to print the LinkedList 
    def printList(self): 
        temp = self.head 
        while(temp): 
            print (temp.data,end=" ") 
            temp = temp.next
  
  
# Driver program to test above functions 
llist = LinkedList() 
llist.push(20) 
llist.push(4) 
llist.push(15) 
llist.push(85) 
  
print ("Given Linked List") 
llist.printList() 
llist.reverse() 
print ("\nReversed Linked List") 
llist.printList() 
  
# This code is contributed by Nikhil Kumar Singh(nickzuck_007) 

Output:

Given Linked List
85 15 4 20 
Reversed Linked List
20 4 15 85

Time Complexity: O(N)

Auxiliary Space: O(1)

A Simpler and Tail Recursive Method

Python3

# Simple and tail recursive Python program to 
# reverse a linked list 
  
# Node class 
  
  
class Node: 
  
    # Constructor to initialize the node object 
    def __init__(self, data): 
        self.data = data 
        self.next = None
  
  
class LinkedList: 
  
    # Function to initialize head 
    def __init__(self): 
        self.head = None
  
    def reverseUtil(self, curr, prev): 
  
        # If last node mark it head 
        if curr.next is None: 
            self.head = curr 
  
            # Update next to prev node 
            curr.next = prev 
            return
  
        # Save curr.next node for recursive call 
        next = curr.next
  
        # And update next 
        curr.next = prev 
  
        self.reverseUtil(next, curr) 
  
    # This function mainly calls reverseUtil() 
    # with previous as None 
  
    def reverse(self): 
        if self.head is None: 
            return
        self.reverseUtil(self.head, None) 
  
    # Function to insert a new node at the beginning 
  
    def push(self, new_data): 
        new_node = Node(new_data) 
        new_node.next = self.head 
        self.head = new_node 
  
    # Utility function to print the LinkedList 
    def printList(self): 
        temp = self.head 
        while(temp): 
            print(temp.data,end=" ") 
            temp = temp.next
  
  
# Driver program 
llist = LinkedList() 
llist.push(8) 
llist.push(7) 
llist.push(6) 
llist.push(5) 
llist.push(4) 
llist.push(3) 
llist.push(2) 
llist.push(1) 
  
print("Given linked list") 
llist.printList() 
  
llist.reverse() 
  
print("\nReverse linked list") 
llist.printList() 
  
# This code is contributed by Nikhil Kumar Singh(nickzuck_007) 

Output

Given linked list
1 2 3 4 5 6 7 8 
Reverse linked list
8 7 6 5 4 3 2 1

Time Complexity: O(N)

Auxiliary Space: O(1)

Please refer complete article on Reverse a linked list for more details!

GeeksforGeeks

Improve

Read List of Dictionaries from File in Python

Python Program for Find largest prime factor of a number

Basic Programs

Array Programs

List Programs

Matrix Programs

String Programs

Dictionary Programs

Tuple Programs

Searching and Sorting Programs

Pattern Printing Programs

Date-Time Programs

Python Regex Programs

Python File Handling Programs

More Python Programs

Python Program to Reverse a linked list

Python3

Python3

Please Login to comment...

Similar Reads

What kind of Experience do you want to share?