【2024考研】题解13 | #删除有序链表重复元素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
        //特例 为空 直接返回
        if(head == NULL || head->next == NULL){
            return head;
        }
        //虚假的表头
        ListNode *dummy = new ListNode(0);
        dummy->next = head;
        //双指针
        ListNode *pre = dummy; 
        ListNode *now = head;
        //开始找抄作业的 now以及now->next都不能空
        while(now != nullptr && now->next != nullptr){
            if(now->val == now->next->val){
                int same = now->val;//记录这个值，检查是否有重复
                //全是重复的情况 now为空也要考虑
                while(now != NULL && now->val == same){
                    ListNode *temp = now;
                    now = now->next;
                    delete temp;
                }
                pre->next = now;
            }
            else{
                pre = now;
                now = now->next;//没找到就都往后走
            }
        }
        ListNode* newHead = dummy->next;
        delete dummy;
        return newHead;//虚假的表头就不用输出了，只是个幌子，只为了抓抄作业的
    }
};