leetcode Remove Duplicates from Sorted Lists

/** * 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 == NULL){            return head;        }        ListNode* tmp = head;        ListNode* next = tmp->next;        //ListNode* prev = tmp;        while(next){            if(next->val == tmp->val){                ListNode*tmpnext = next->next;                tmp->next = tmpnext;                delete next;                next = tmpnext;            }            else{                tmp = next;                next = next->next;            }        }        return head;    }};