class Solution {
    ListNode p1 ;
    public ListNode reverseList(ListNode head) {          
                ListNode p  = head;     
                while(p!=null){               
                    addFirst(p.val);                 
                    p = p.next;
                }
                return p1;
    }
    void addFirst(int a){
        ListNode renode=new ListNode(a);
        if(p1!=null){
             renode.next = p1;
        }
        p1 = renode; 
    }
}