82. 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 *dummy = new ListNode(-1);
        dummy->next = head;
        ListNode *pre = dummy;
        ListNode *cur = dummy->next;
        
        while(cur){
            while(cur->next && cur->next->val == pre->next->val)
            {
                cur = cur->next;
            }    
            if(pre->next == cur)
                pre = pre->next;
            else
                pre->next = cur->next;
            cur = cur->next;
        }
        return dummy->next;
        
    }
};