/**
 * 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)
            return head;
        ListNode* newHead=new ListNode(-1);
        newHead->next=head;
        ListNode* p0=head;
        ListNode* p1=head;
        
        while(p0->next!=NULL){
            if(p1==NULL){
                p0->next=NULL;
                break;
            }
            if(p0->val==p1->val){
                p1=p1->next;
            }else{
                p0->next=p1;
                p0=p1;
            }
        }
        head=newHead->next;
        delete newHead;
        return head;
    }
};