Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

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

/**
 * 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){
        if(!head) return head;
    
        ListNode* cur = head->next;
        ListNode* pre = head;
        while(cur){
            if(cur->val == pre->val){
                pre->next = cur->next;
                delete cur;
            }else{
                pre = pre->next;
            }
            cur = cur->next;
        }
        return head;
    }
};