#206. Reverse Linked List | LeetCode Python Solution

Problem

LeetCode Problem

206. Reverse Linked List

Python Solution

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        """ Excalidraw
        https://excalidraw.com/#json=UqvQowXkhpfENtThTOs_E,1B3hSOle-aV0zqAwzWQRGA
        """

        # Return immediately if the linked list is empty
        if head is None:
            return head

        # Initialize current node pointer 'c' and next node pointer 'n'
        c = head
        n = c.next

        # Make first node point to None
        c.next = None

        # Loop until next node pointer is None.
        while n is not None:
            # Save the pointer to next node
            tmp = n.next

            # Reverse link
            n.next = c

            # Advance to next pair of nodes
            c = n
            n = tmp

        # 'c' is the new head so point 'head' to it
        head = c

        return head