每天一算：Reverse Linked List

 1// 206. Reverse Linked List
 2// https://leetcode.com/problems/reverse-linked-list/description/
 3//
 4// 递归的方式反转链表
 5// 时间复杂度: O(n)
 6// 空间复杂度: O(1)
 7class Solution {
 8public:
 9    ListNode* reverseList(ListNode* head) {
10
11        // 递归终止条件
12        if(head == NULL || head->next == NULL)
13            return head;
14
15        ListNode* rhead = reverseList(head->next);
16
17        // head->next此刻指向head后面的链表的尾节点
18        // head->next->next = head把head节点放在了尾部
19        head->next->next = head;
20        head->next = NULL;
21
22        return rhead;
23    }
24};