leetcode 19: 删除链表的倒数第N个节点

 1 ListNode* removeNthFromEnd(ListNode* head, int n) {
 2     ListNode *p = head, *q = head; 
 3     while(n-- > 0 && nullptr != p)
 4     {
 5          p = p->next;
 6     }
 7     if(n <= 0)
 8     {
 9         if(p == nullptr)
10             return q->next;
11         while(p->next != nullptr)
12         {
13             p = p->next;
14             q = q->next;
15         }
16         q->next = q->next->next;
17     }
18     return head;
19 }