Knowledge base:
ListNode traverse using while loop with node.next!=null
delete node.next=node.next.next
traverse node=node.next
public ListNode deleteDuplicates(ListNode head) {
if(head==null||head.next==null) return head;
ListNode res=head;
while(res.next!=null){
if(res.val==res.next.val)
res.next=res.next.next;
else
res=res.next;
}
return head;
}
