/
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/

class Solution {
    public:
ListNode* deleteDuplication(ListNode* head) {
    ListNode* f = NULL;
    ListNode* s =NULL;
    ListNode* p =NULL;
    bool flag = false;
    if (head==NULL) return head;
    if (head->next == NULL) return head;

    while(head!=NULL && head->next!=NULL && head->val == head->next->val ){
        f = head -> next;
        while(f!=NULL&&head->val == f->val){
        f = f->next;
        }
        head = f;
    }
    if (head ==NULL || head -> next== NULL) return head;
    // cout<<head<<endl;
    s = head->next;
    p = head;
    while(s!=NULL && s->next!=NULL ){
        // cout<<s->val<<endl;
        ListNode* s1 = s->next;
        if (s->val == s1->val){
            // cout<<1<<endl;
           while(s->val == s1->val ){
                if (s1->next!=NULL){
                     s1 = s1->next;
                    //  cout<<s1->val<<endl;
                }

                else
                    {
                        flag = true;
                        break;
                    }
            }
           s->val = s1 ->val;
           s ->next = s1->next;
           continue;
        }
        s = s -> next;
    }
    if (flag){
        s = head;
        p = head->next;
        if (p == NULL && s == head ) {
            head->next = NULL;
        }
        while(p->next!=NULL){
            p = p->next;
            s = s->next;
        }
        s -> next = NULL;
    }
    // s = head->next;
    // f = head;
    // while( s != NULL ){
    //     if (s == head){
    //         f -> next=NULL;
    //     }
    //     f = f->next;
    //     s = s->next;
    // }

    return head;
}

};