Reverse Linked List Iteratively and Recursively

McAfee security components may represent ordered alerts as singly linked lists. Implement reverse_linked_list so it can reverse the list using either an iterative pointer update or a recursive approach.

Formal Specification

The input is the head of a singly linked list whose nodes contain an integer val and a next pointer. The function must return the head of the reversed list. When recursive is False, use an iterative algorithm. When it is True, use recursion. Reverse the existing nodes in place rather than creating replacement nodes.

For testing, a list such as [1, 2, 3] represents nodes linked in that order, and the returned list is serialized back to an array.

Constraints

0 <= n <= 10^5
-10^9 <= node.val <= 10^9
The linked list contains no cycles
Reverse nodes in place without creating replacement nodes

Function Signature

def reverse_linked_list(head, recursive=False):

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