题解 | #删除有序链表中重复的元素-II#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    ListNode* deleteDuplicates(ListNode* head) {
        // write code here
        //保留原链表中只存在一次的元素结点  可能会删除头结点 所以做一个虚拟头结点  
        if(head == nullptr || head->next == nullptr) return head;
        ListNode temp(-1);
        temp.next = head;
        ListNode* virhead = &temp;
        ListNode* p = virhead;
		//处理head链表
        while(p->next != nullptr && p->next->next != nullptr)
        {           
		  //如果有相同元素
            if(p->next->val == p->next->next->val)
            {
			  //找出是不是相同元素的范围 p --- last 前开后闭区间 
                ListNode* last = p->next->next;
                while(last->next != nullptr &&last->next->val == p->next->val)
                {
                    last = last->next;
                }
			  //删除这个区间
                ListNode* del = p->next;
                while(del != last)
                {
                    p->next = del->next;
                    delete  del;
                    del = p->next;
                }
                del = p->next;
                p->next = del->next;
                delete del;
                continue;
            }
            p = p->next;
        }

        return virhead->next;

    }
};