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(NULL != head){
            ListNode *p = head;
            while(NULL != p){
                ListNode *n = p->next;
                if(NULL == n) break;
                if(n->val == p->val) p->next = n->next;
                else p = p->next;
            }
        }
        return head;
    }
};