0206. 反转链表

1, 题目

反转一个单链表。

示例:

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

进阶:
你可以迭代或递归地反转链表。你能否用两种方法解决这道题？

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/reverse-linked-list
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

2, 算法

object Solution {
    def reverseList(head: ListNode): ListNode = {
        val result = new ListNode()
        var current = head
        while (current != null) {
            val t = current
            current = current.next
            t.next = null
            t.next = result.next
            result.next = t
        }
        val x = result.next
        result.next = null
        x
    }
}

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        result = ListNode()
        while head:
            t = head
            head = head.next
            t.next = None
            t.next = result.next
            result.next = t
        head = result.next
        result.next = None
        return head