[leetcode 206] Reverse Linked List

ListNode* reverseList(ListNode* head)
{
if (!head || !head->next)
return head;

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

return head;
}