mq030.反转链表

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

class Solution:
    def reverseList1(self, head: ListNode) -> ListNode:
        prev = None
        while head is not None:
            tmp = head.next
            head.next = prev
            prev = head
            head = tmp
        return prev

    def reverseList2(self, head: ListNode) -> ListNode:
        if not head or not head.next:
            return head

        p = self.reverseList(head.next)
        head.next.next = head
        head.next = None
        return p