剑指 Offer 24. 反转链表

思路

1. 递归

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        def helper(head):
            if head is None or head.next is None:
                return head
            ret = helper(head.next)
            head.next.next = head
            head.next = None
            return ret
        return helper(head)

2. 双指针

# TODO