Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

/**
 * 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 || !head->next) return head;
        ListNode* newHead = new ListNode(-1);
        newHead->next = head;
        ListNode* pre = newHead;
        ListNode* cur = head;
        bool duplicated = false;// if has duplicates
        while(cur->next){
            if(cur->val == cur->next->val){
                cur = cur->next;
                duplicated = true;
            }else{
                if(duplicated){
                    while(pre->next != cur->next){
                        ListNode* tmp = pre->next;
                        pre->next = pre->next->next;
                        delete tmp;
                    }
                //     pre->next = cur->next;
                    duplicated = false;
                }else{
                    pre->next = cur;
                    pre = cur;
                }
                cur = cur->next;
            }
        }
        if(duplicated){
            pre->next = nullptr;
        }
        return newHead->next;
    }
};