/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* filterList(ListNode* head) {
        int a[10010] = {0};

        auto p = head;

        auto pre = head;
        while(p != NULL)
        {
            int data = abs(p->val);
            if(a[data] == 1)
            {
                pre->next = p->next;
                auto tmp = p;
                p = p->next;
                delete(tmp);
            }else
            {
                a[data] = 1;
                pre = p;
                p = p->next;
            }
        }

        return head;
    }
};