Leetcode 206 Reverse Linked List

Reverse a singly linked list.

Hint:

A linked list can be reversed either iteratively or recursively. Could you implement both?

题目大意：反转单链表

提示：

反转一个链表可以用迭代或者递归的方法。你能都实现吗？

递归：

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* reverseList(ListNode* head) {
12         //最后一个节点会返回，作为头结点
13         if(head == NULL || head -> next == NULL)
14             return head;
15         //head->next 表示剩下的部分
16         ListNode* newHead = reverseList(head -> next);
17         head -> next -> next = head;
18         head -> next = NULL;
19         return newHead;
20     }
21 };

迭代：