remove-duplicates-from-sorted-list

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

For example,
Given1->1->2, return1->2.
Given1->1->2->3->3, return1->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 *dummy = new ListNode(-1);
        dummy->next = head;
        ListNode *p = head;
        ListNode *pre = dummy;
        
        while(p&&p->next){
               if(p->val==p->next->val){
                pre->next = p->next;
                p = p->next;
            }else{
                pre = p;
                p = p->next;
            }
        }
        
        return dummy->next;
    }
};