【剑指offer】十，反转链表

 1 /*
 2 public class ListNode {
 3     int val;
 4     ListNode next = null;
 5  
 6     ListNode(int val) {
 7         this.val = val;
 8     }
 9 }*/
10 public class Solution {
11     public ListNode ReverseList(ListNode head) {
12         if(head ==null){
13             return null ;
14         }
15         ListNode l2 = null ;
16         ListNode l2head = l2 ;
17         while(head!=null){
18             ListNode temp = head.next  ;
19             head.next = l2 ;
20             l2 = head ;
21             head = temp ;
22         }
23          
24         return l2 ;
25     }
26 }