public ListNode deleteDuplicates(ListNode head) {
        ListNode x=head;
        while(x!=null){
            if(x.next!=null && x.val==x.next.val){
                x.next=x.next.next;
            }else{
                x=x.next;
            }
        }
        return head;
    }
Given a sorted linked list, delete all duplicates such that each element appear only once.
For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.->3
src/problems/easy/RemoveDuplicatesLinkedList.java