题目描述
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：
输入：head = [1,2,3,4,5]
输出：[5,4,3,2,1]
示例 2：
输入：head = [1,2]
输出：[2,1]
示例 3：
输入：head = []
输出：[]
思路&js代码
1、迭代
var reverseList = function (head) {
let prev = null
let curr = head
while (curr) {
const tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
}
return prev
};