递归反转单链表。
ListNode *reverseList(ListNode *head,ListNode *pNewHead)
{
if(head == NULL)
return pNewHead;
ListNode *next = head->next;
head->next = pNewHead;
return reverseList(next,head);
}
ListNode* reverseList(ListNode* head) {
return reverseList(head,NULL);
}