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Question:
How to Reverse a sublist of a linked list in Python?

Summary: 

The problem of reversing a linked list between specified positions is addressed by the Python code that is presented here. Changing the order of the nodes in a given linked list from position "left" to position "right" is the problem statement that needs to be understood.


Solution:

#User function Template for python3


'''

# Node Class

class Node:

    def __init__(self, data):   # data -> value stored in node

        self.data = data

        self.next = None

'''


class Solution:

    

    def reverseBetween(self, head,left,right):

        if not head or left == right:

            return head

    

        dummy = Node(0)

        dummy.next = head

        pre = dummy

    

        # Move to the position just before the reversal starts

        for _ in range(left - 1):

            pre = pre.next

    

        # Reverse the nodes from left to right

        current = pre.next

        next_node = None

        for _ in range(right - left + 1):

            temp = current.next

            current.next = next_node

            next_node = current

            current = temp

    

        # Update pointers

        pre.next.next = current

        pre.next = next_node

    

        return dummy.next


Explanation:

The above codes contains a method named reverseBetween, which takes three parameters - head (the head of the linked list), left (the left position of the reversal), and right (the right position of the reversal).

  • It first checks if the linked list is empty or if the left and right positions are the same. If either condition is true, it returns the original linked list.

  • A dummy node is created, and its next is set to the head of the linked list. This dummy node helps in handling edge cases where the reversal starts from the beginning of the linked list.

  • The code then moves to the position just before the reversal starts by iterating through the linked list.

  • The nodes from position 'left' to position 'right' are reversed using a simple iterative reversal technique.

  • Pointers are updated to connect the reversed portion back to the original linked list.

  • Finally, the modified linked list is returned.


Answered by: >shripalle

Credit: >GeekforGeeks


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