Reverse a Linked List - Python

Last Updated : 21 Feb, 2025

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: 1 -> 2 -> 3 -> 4 -> NULL
Output: head: 4 -> 3 -> 2 -> 1 -> NULL
Explanation: Reversed Linked List:
Reversed Linked List

Input: head: 1 -> 2 -> 3 -> 4 -> 5 -> NULL
Output: head: 5 -> 4 -> 3 -> 2 -> 1 -> NULL
Explanation: Reversed Linked List:
Reversed Linked List
Input : NULL
Output : NULL

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

1. Iterative Method

The idea is to reverse the links of all nodes using three pointers:
prev: pointer to keep track of the previous node
curr: pointer to keep track of the current node
next: pointer to keep track of the next node
Starting from the first node, initialize curr with the head of linked list and next with the next node of curr. Update the next pointer of curr with prev. Finally, move the three pointer by updating prev with curr and curr with next.

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()

 
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 functionsllist = 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()

Output

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

Time Complexity: O(N)
Auxiliary Space: O(1)

2. A Simpler and Tail Recursive Method

The idea is to reach the last node of the linked list using recursion then start reversing the linked list from the last node.

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()

 
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 programllist = 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()

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 Reverse a linked list for more details!

Reverse a Linked List - Python

kartik

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Reverse a Linked List - Python

1. Iterative Method

2. A Simpler and Tail Recursive Method

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