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

ListNode(int val) {
    this.val = val;
}
}*/
public class Solution {
public ListNode ReverseList(ListNode head) {
    if(head==null||head.next==null){
        return head;
    }
    ListNode pre=null;
    ListNode next=null;
    while(head!=null){
        next = head.next;
        head.next = pre;
        pre = head;
        head = next;
    }
    return pre;
}
}