面试题16：反转链表

/*public class ListNode {    int val;    ListNode next = null;    ListNode(int val) {        this.val = val;    }}*/public class Solution {    public ListNode ReverseList(ListNode head) {        ListNode reversedHead=null;        ListNode currentNode=head;        ListNode preNode=null;                while(currentNode!=null){            ListNode temp=currentNode.next;            if(temp==null)                reversedHead=temp;//尾结点            currentNode.next=preNode;                        preNode=currentNode;            currentNode=temp;        }        return preNode;    }}