反转一个单链表。

示例:

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

 

 

 

 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
       ListNode prev=null;
       ListNode cur=head;
       while(cur!=null){
           ListNode nextNode=cur.next;
           cur.next=prev;
           prev=cur;
           cur=nextNode;
       }
       return prev;
    }
}