leetcode 38: Remove Duplicates from Sorted 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function    
        if(!head) return head;
        
        int val = head->val;       
        ListNode ** pp = &head;
        ListNode * cur = head;
        
        if( cur->next == NULL || cur->next->val != cur->val  ) {
            *pp = cur;
            pp = &(cur->next);
        }
    
        while( (cur=cur->next) != NULL  ) {
            if( cur->val != val) {
                if( cur->next == NULL || cur->next->val != cur->val) {
                    *pp = cur;
                    pp = &(cur->next);
                }
                val = cur->val;
            }
        }
        
        *pp = NULL;
        return head;
    }
};