import java.util.*;/* * public class ListNode { *   int val; *   ListNode next = null; *   public ListNode(int val) { *     this.val = val; *   } * } */public class Solution { public static ListNode ReverseList(ListNode head) {            if(head==null)            return null;            ListNode reversedHead=null;            ListNode current=head;            ListNode tmp=null;                    //循环遍历节点            while(current!=null){                // 将节点赋予temp            tmp= current;            //            current= current.next;            //将节点尾指针置为空            tmp.next=null;            //判断反转链表是否为空            if(reversedHead==null)            reversedHead=tmp;            //否则按照头插法插入            else{                tmp.next=reversedHead;                reversedHead=tmp;            }                 }             //返回头节点            return reversedHead;     }}