反转链表

struct ListNode
{
      int       val_;
      ListNode* next;
	  ListNode(int val): val_(val),next(NULL){}
};
//非递归
ListNode *reverse(ListNode *head)
{
	if(head == NULL) return NULL;
	
	ListNode* vir = new ListNode(0);
	vir->next = NULL;
	ListNode *p = head;
	
	while(p != NULL)){
		ListNode *q = p->next;
		p->next = vir->next;
		vir->next = p;
		p = q;
	}
	
	head = vir->next;
	delete vir;
	return head;
} 
//递归
ListNode *reverse(ListNode *head)
{
	if(head == NULL)
	  return NULL;
	if(head->next == NULL)
		return head;

	ListNode *tp = head->next;
	ListNode *p = reverse(tp);
	tp->next = head;
	head->next = NULL;
	
    
	return p;
}