leetcode_remove_duplicates_from_sorted_list_ii

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode *dummy = new ListNode(-1), *current = dummy;
        dummy->next = head;
        while(current->next != NULL && current->next->next != NULL)
        {
            ListNode *current_n = current->next;
            ListNode *current_n_n = current_n->next;
            if(current_n ->val == current_n_n->val)
            {
                int value = current_n_n->val;
                while(current_n_n->next != NULL && current_n_n->next->val == value)
                {
                    current_n_n = current_n_n->next;
                }
                current->next = current_n_n->next;
            }
            else
            {
                current = current->next;
            }
        }
        return dummy->next;
    }
};