/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* deleteDuplicates(ListNode* head) {
if(head == NULL || head->next == NULL) return head;
head->next = deleteDuplicates(head->next);
if(head->val == head->next->val) head = head->next;
return head;
}
};