【剑指OFFER】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 || head.next == null) return head;
13         ListNode pre = null;
14         ListNode next = null;
15         while (head != null) {
16             next = head.next;
17             head.next = pre;
18             pre = head;
19             head = next;
20         }
21         return pre;
22     }
23 }