[LeetCode] Remove Duplicate from Sorted Linkded List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 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) {        // IMPORTANT: Please reset any member data you declared, as        // the same Solution instance will be reused for each test case.        if(head==NULL)            return head;                ListNode *p1=NULL;        ListNode *p2=head;                while(p2!=NULL)        {            if(p2->next==NULL || (p2->next!=NULL && p2->val!=p2->next->val) )            {                if(p1==NULL)                {                    p1=new ListNode(0);                    p1=p2;                    head=p1;                }                else{                    p1->next=p2;                    p1=p2;                }                        p2=p2->next;                        //if(p2!=NULL && p2->next!=NULL)                  //  p1->next=NULL;                        continue;            }                                int dup=p2->val;            while(p2!=NULL && p2->val==dup)            {                if(p1!=NULL)                    p1->next=NULL;                ListNode *tmp=p2;                p2=p2->next;                delete tmp;            }        }                if(p1==NULL) return NULL;                return head;    }};