/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode ReverseList(ListNode head) {
        ListNode pre=null;
        ListNode next=null;
        while(head!=null){
            next=head.next;   首先保存后边的结点
            head.next=pre;     
            pre=head;
            head=next;
        }
        return pre;

    }
}