[LeetCode] Reverse Linked List

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* reverseList(ListNode* head) {
if (head == NULL) return NULL;

ListNode* p = head->next;
head->next = NULL;

while (p != NULL) {
ListNode* q = p->next;
p->next = head;
head = p;
p = q;
}

return head;
}
};