83. Remove Duplicates from Sorted List

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 static int wing=[]()
10 {
11     std::ios::sync_with_stdio(false);
12     cin.tie(NULL);
13     return 0;
14 }();
15 
16 
17 class Solution 
18 {
19 public:
20     ListNode* deleteDuplicates(ListNode* head) 
21     {
22         if(head==NULL||head->next==NULL)
23             return head;
24         ListNode *pre=head,*beh=head->next;
25         while(beh)
26         {
27             if(pre->val==beh->val)
28             {
29                 beh=beh->next;
30                 pre->next=beh;
31             }
32             else
33             {
34                 pre=beh;
35                 beh=beh->next;
36             }
37         }
38         return head;
39     }
40 };

Two pointers, compare the values ​​of the front and back nodes, if they are equal, the back pointer moves back, and the successor of the front pointer moves back subsequently

If they are not equal, the two pointers are moved backward at the same time, until the latter pointer is empty, indicating that the linked list is scanned.