题目：

题解：

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:newHead = ListNode(0)newHead.next = Noneh = headwhile h:cur = ListNode(h.val)cur.next = newHead.nextnewHead.next = curh = h.nextreturn newHead.next