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

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        if not head:
            return None
        p = ListNode(head.val)
        p.next = None
        while head.next != None:
            head = head.next
            tmp = ListNode(head.val)
            tmp.next = p
            p = tmp
        return p