leetcode链表--18、remove-nth-node-from-end-of-list（从链表中删除倒数第k个结点）

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode *removeNthFromEnd(ListNode *head, int n) {
12         if(head == NULL)
13             return NULL;
14         ListNode *pPre = NULL;
15         ListNode *p1 = head;
16         ListNode *p2 = head;
17         for(int i=0;i<n-1;i++)
18         {
19             p2 = p2->next;
20         }
21         while(p2->next != NULL)
22         {
23             pPre = p1;
24             p1 = p1->next;
25             p2 = p2->next;
26         }
27         if (pPre == NULL)//正好要删除的就是第一个结点
28         {
29             head = p1->next;
30             delete p1;
31         }
32         else
33         {
34            pPre->next = p1->next;
35            delete p1;
36         }
37  
38         return head;
39     }
40 };