82. Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

同样使用二级指针，比我之前在牛客网上做这道题的方法简便了好多。这又是一大进步。

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode** pp = &head;
        bool deleted = false;

        while((*pp) != NULL){
            if((*pp)->next == NULL){
                if(deleted) *pp = NULL;
                break;
            }

            if((*pp)->val == (*pp)->next->val){
                ListNode* tmp = (*pp)->next;
                (*pp)->next = tmp->next;
                delete tmp;
                deleted = true;
            }
            else if(deleted){
                (*pp) = (*pp)->next; //删除重复元素的第一个
                deleted = false;
            }
            else{
                pp = &((*pp)->next);
            }
        }

        return head;
    }
};