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  1. class ListNode:
  2.     """Definition for singly-linked list node."""
  3.     def __init__(self, value=0, next=None):
  4.         self.value = value
  5.         self.next = next
  6.  
  7. def reverse_linked_list(head):
  8.     """
  9.     Reverses a singly linked list.
  10.  
  11.     Args:
  12.         head (ListNode): The head of the linked list.
  13.  
  14.     Returns:
  15.         ListNode: The new head of the reversed list.
  16.     """
  17.     prev = None
  18.     current = head
  19.  
  20.     while current:
  21.         next_node = current.next  # store next node
  22.         current.next = prev       # reverse the link
  23.         prev = current            # move prev forward
  24.         current = next_node       # move current forward
  25.  
  26.     return prev
  27.  
  28. # Helper to create a linked list from a list of values
  29. def create_linked_list(values):
  30.     if not values:
  31.         return None
  32.     head = ListNode(values[0])
  33.     current = head
  34.     for val in values[1:]:
  35.         current.next = ListNode(val)
  36.         current = current.next
  37.     return head
  38.  
  39. # Helper to convert linked list to list (for display)
  40. def linked_list_to_list(head):
  41.     result = []
  42.     while head:
  43.         result.append(head.value)
  44.         head = head.next
  45.     return result
  46.  
  47. original = create_linked_list([1, 2, 3, 4, 5])
  48. reversed_head = reverse_linked_list(original)
  49. print(linked_list_to_list(reversed_head))  # Output: [5, 4, 3, 2, 1]
Success #stdin #stdout 0.04s 9404KB
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Standard input is empty
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[5, 4, 3, 2, 1]
https://ideone.com/KfE3CH
language:
Python 3 nbc (python 3.7.3)
created:
4 days ago
visibility:
public

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