82. 删除排序链表中的重复元素 II

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode* newHead = new ListNode(0, head);
        ListNode *p = newHead, *q, *t;
        while(p->next) {
            t = p->next;
            for(q = t->next; q && q->val == t->val; q = q->next);
            if(t->next == q) {
                p->next = t;
                p = p->next;
            }
            else p->next = q;
        }
        return newHead->next;
    }
};