83. Remove Duplicates from Sorted List

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if(head == NULL) return head;
        ListNode* head_tmp = head;
        while(head->next != NULL){
            if(head->val == head->next->val) head->next = head->next->next; 
            else head = head->next;
        }
        return head_tmp;
    }
};