LeetCode(82)题解: Remove Duplicates from Sorted List II

https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/

题目：

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.

思路：

需要两个指针，a用来纪录新链表，b用来遍历老链表，因为只有删除操作，需要一个flag标记ab段要不要删除。此外要注意头节点的处理。

AC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==NULL)
             return NULL;
         ListNode* newhead=new ListNode();  // to handle head
         newhead->next=head;
         ListNode* a=newhead,*b=newhead->next;
         int now=head->val;
         bool occur_flag=false;
         while(b->next!=NULL){
             if(b->next->val==now){
                 occur_flag=true;
             }
             else{
                 if(occur_flag==true){
                     a->next=b->next;  //delete duplicate numbers
                     b=a;    //update pointers
                 }
                 else{
                     a=b;
                 }
                 occur_flag=false;
                 now=b->next->val;
             }
             b=b->next;
         }
         if(occur_flag==true){
             a->next=b->next;  //delete duplicate numbers
             b=a;    //update pointers
         }
         else{
             a=b;
         }
         return newhead->next;
     }
 };