题解 | #删除有序链表中重复的元素-II#

/**
 * struct ListNode {
 *  int val;
 *  struct ListNode *next;
 *  ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @return ListNode类
     */
    ListNode* deleteDuplicates(ListNode* head) {
        // write code here
        auto *first=new ListNode(0);
        first->next=head;
        ListNode* p = first;
        ListNode* pre, *cur;
        // if (p ->next == nullptr)
        //     return nullptr;
        pre=p->next;
        cur=pre->next;
        while (pre) {
            int flag=0;
            while (cur && pre->val == cur->val) {
                pre->next = cur->next;
                cur = pre->next;
                flag=1;
            }
            if(flag){
                p->next=pre->next;
                pre=p->next;
                cur=pre->next;
            }
            else{
                p=p->next;
                pre=pre->next;
                cur=pre->next;
            }
        }
        return first->next;
    }
};