[LeetCode] Reverse Linked List

 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         if (head == NULL) return NULL;
13         
14         ListNode* p = head->next;
15         head->next = NULL;
16         
17         while (p != NULL) {
18             ListNode* q = p->next;
19             p->next = head;
20             head = p;
21             p = q;
22         }
23         
24         return head;
25     }
26 };