题目链接：https://www.acwing.com/problem/content/27/
题目如下：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplication(ListNode* head) {
        ListNode* dummy=new ListNode(-1);
        dummy->next=head;
        head=dummy;
        ListNode* pre=dummy;
        
        while(pre->next&&pre->next->next){
            if(pre->next->val==pre->next->next->val){
                //如果当前pre->next和pre->next->next对应的元素相同，需要将pre->next以及所有后面拥有相同元素值的链表节点全部删除
                //方法：记下这个元素值，随后将当前节点pre->next从链表中移除，直到为空节点或者其元素值不等于x为止
                int temp=pre->next->val;
                
                while(pre->next&&pre->next->val==temp){
                    pre->next=pre->next->next;
                }
            }
            else {
                pre=pre->next;
            }
        }
        return dummy->next;
    }
};