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.

class Solution {public:    ListNode *deleteDuplicates(ListNode *head) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        ListNode dy_node(0), *q = &dy_node;        ListNode de_node(0), *q1 = &de_node;        int last = INT_MAX;        for(ListNode *p = head; p; p = p->next){            if (last != p->val){                q = q->next = p;                last = p->val;            }else{                q1 = q1->next = p;            }            }        q->next = NULL;        q1->next = NULL;        /*        ListNode *p = de_node.next;        while(p){            ListNode *temp = p->next;            delete p;            p = temp;        }*/        return dy_node.next;    }};