Reverse a singly linked list.
Hint:
A linked list can be reversed either iteratively or recursively. Could you implement both?
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Solving method:
class ListNode(object): def __init__(self, x): self.val = x self.next = None class Solution(object): def reverseList(self, head): result = ListNode(None) while head: next = head.next head.next = result.next result.next = head head = next return result.next