删除链表中倒数第n个节点

 1 /**
 2  * Definition of ListNode
 3  * class ListNode {
 4  * public:
 5  *     int val;
 6  *     ListNode *next;
 7  *     ListNode(int val) {
 8  *         this->val = val;
 9  *         this->next = NULL;
10  *     }
11  * }
12  */
13 class Solution {
14 public:
15     /**
16      * @param head: The first node of linked list.
17      * @param n: An integer.
18      * @return: The head of linked list.
19      */
20     ListNode *removeNthFromEnd(ListNode *head, int n) {
21         // write your code here
22         if(n > 0)  {
23             ListNode *pBegin=head, *pEnd=head;
24             while(n-- && pEnd!=NULL) {
25                 pEnd = pEnd->next;
26             }
27             //  n<链表长度
28             if(n == -1 && pEnd!=NULL) {
29                 while(pEnd->next != NULL)  {
30                     pBegin = pBegin->next;
31                     pEnd = pEnd->next;
32                 }
33                 pBegin->next = pBegin->next->next;
34                 return head;
35             }
36             //  n>链表长度
37             else if(n > -1 && pEnd!=NULL)  {
38                 return head;
39             }
40             //  n=链表长度
41             else  {
42                 return head->next;
43             }
44         }
45     }
46 };