链表反转

 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* reverse(ListNode* cur, ListNode* pre) {
12         if (cur == NULL) {
13             return pre;
14         }
15         ListNode* res = reverse(cur->next, cur);
16         cur->next = pre;
17         return res;
18     }
19     /*这里返回 res 是为了在链表多次递归返回后依旧能够保存递归深层次的链表节点值*/
20     ListNode* reverseList(ListNode* head) {
21         ListNode* res = reverse(head, NULL);
22         return res;
23     }
24 };