Remove Duplicates from Sorted List

/**
 * 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 *current = NULL;
        ListNode *anterior = NULL;
        current = head;
        while(current){
            if(anterior != NULL && current->val == anterior->val){
                anterior->next = current->next;
            }else anterior = current;
            current = current->next;
        }
        return head;
    }
};