leetcode/206_reverse_linked_list.py at main · motdam/leetcode · GitHub

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from utils.helpers import ListNode, create_linked_list, print_linked_list
from typing import List, Optional


class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        prev, current = None, head
        while current:
            next = current.next
            current.next = prev
            prev = current
            current = next
        return prev


if __name__ == "__main__":
    # Test case 1: Basic reversal
    values = [1, 2, 3, 4, 5]
    linked_list = create_linked_list(values)

    solution = Solution()
    reversed_list = solution.reverseList(linked_list)

    print(f"Original list: {values}")
    print(f"Reversed list: {print_linked_list(reversed_list)}")

    # Test case 2: Single element
    single_value = create_linked_list([1])
    reversed_single = solution.reverseList(single_value)
    print(f"\nSingle element test:")
    print(f"Reversed list: {print_linked_list(reversed_single)}")

    # Test case 3: Empty list
    empty_list = create_linked_list([])
    reversed_empty = solution.reverseList(empty_list)
    print(f"\nEmpty list test:")
    print(f"Reversed list: {print_linked_list(reversed_empty)}")