82

/**
 * 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 *dummy = new ListNode(0, head);
        ListNode *pre = dummy;
        while(head){
            if(head->next && head->val == head->next->val){
                while(head->next && head->val == head->next->val) head = head->next;
                pre->next = head->next;
            }
            else{
                pre = pre->next;
            }
            head = head->next;
        }
        return dummy->next;
    }
};