206. 反转链表

题目描述

 反转一个单链表。

原题请参考链接https://leetcode-cn.com/problems/reverse-linked-list/

题解

方法一 【迭代(双指针)】

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        pre = None
        cur = head
        while cur:
            tmp = cur.next
            cur.next = pre
            pre = cur
            cur = tmp
        return pre 

方法二 【递归】

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