leetcode 19.删除链表的倒数第N个节点

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9  //双指针法
10 class Solution {
11     public ListNode removeNthFromEnd(ListNode head, int n) {
12         if(null==head){
13             return head;
14         }
15         ListNode iterator = head;
16         ListNode pre = null;
17         ListNode slowIterator = head;
18         int i=1;
19         while(iterator.next!=null){
20             if(i==n){
21                 pre=head;
22                 iterator=iterator.next;
23                 slowIterator=slowIterator.next;
24                 i++;
25             }else if(i<n){
26                 iterator=iterator.next;
27                 i++;
28             }else{
29                 pre=slowIterator;
30                 iterator=iterator.next;
31                 slowIterator=slowIterator.next;
32                 i++;
33             }
34         }
35         if(pre==null){
36             return head.next;
37         }else{
38             pre.next=slowIterator.next;
39             return head;
40         }
41     }
42 }