/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode* dumyHead = new ListNode(512);
        dumyHead->next = head;

        ListNode* preHead = dumyHead;
        ListNode* currentHead = head;
        while(currentHead != NULL)
        {
            if(preHead->val == currentHead->val)
            {
                preHead->next = currentHead->next;
                currentHead = preHead->next;
            }
            else
            {
                preHead = preHead->next;
                currentHead = currentHead->next;
            }
        }
        return dumyHead->next;

    }
}