Remove Duplicates from Sorted List [LEETCODE]

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.

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Nothing, patience, AC once.

/**
 * 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) return NULL;
        if(NULL == head->next) return head;
        ListNode *p1 = head;
        ListNode *p2 = head->next;
        while(p1 && p2){
            if(p1->val == p2->val){
                p1->next = p2->next;
                p2 = p1->next;
            }else{
                p1 = p1->next;
                p2 = p2->next;
            }
            
        }
        return head;
    }
};