反转链表 #

给你单链表的头节点 head ，请你反转链表，并返回反转后的链表。 示例 1： ```shell 输入：head = [1,2,3,4,5] 输出：[5,4,3,2,1] ``` 示例 2： ```shell 输入：head = [1,2] 输出：[2,1] ``` 示例 3： ```shell 输入：head = [] 输出：[] ``` 提示： ```shell 链表中节点的数目范围是 [0, 5000] -5000 <= Node.val <= 5000 ``` 进阶：链表可以选用迭代或递归方式完成反转。你能否用两种方法解决这道题？

Given the head of a singly linked list, reverse the list, and return the reversed list. Example 1: ``` Input: head = [1,2,3,4,5] Output: [5,4,3,2,1] ``` Example 2: ``` Input: head = [1,2] Output: [2,1] ``` Example 3: ``` Input: head = [] Output: [] ``` Constraints: ``` The number of nodes in the list is the range [0, 5000]. -5000 <= Node.val <= 5000 ``` Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?

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```go /** * Definition for singly-linked list. * type ListNode struct { * Val int * Next *ListNode * } */ func reverseList(head *ListNode) *ListNode { var pre *ListNode = nil var next *ListNode = nil var cur *ListNode = head for cur != nil { next = cur.Next cur.Next = pre pre = cur cur = next } return pre } ```

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