Leetcode: 82. Remove Duplicates from Sorted List II

Description

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

Example

Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

思路

• 链表去重，一旦重复，所有的重复节点都删除
• 注意删除后为空的情况，和头结点删除的时候

代码

/**
 * 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 NULL;
        ListNode *ptr = head, *pNext = head->next;
        ListNode *res = new ListNode(0);
        ListNode *h = res;
        
        while(pNext){
           if(pNext->val == ptr->val){
               do{
                    ListNode *tmp = pNext;
                    pNext = pNext->next;
                    delete tmp;
               }while(pNext && pNext->val == ptr->val);
              delete ptr;
              ptr = pNext;
              if(ptr)
                pNext = ptr->next;
           }
           else{
               res->next = ptr;
               res = res->next;
               ptr = pNext;
               pNext = ptr->next;
           }
        }
        
        if(ptr && res && res->val != ptr->val){
            res->next = ptr;
            res = res->next;
        }
        
        if(res)
            res->next = NULL;
        
        return h->next;
    }
};