Remove Duplicates from Sorted List

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { *         val = x; *         next = null; *     } * } */public class Solution {    public ListNode deleteDuplicates(ListNode head) {        //貌似也是双指针,其实不懂这算不算双指针，反正用两个点mark着        if(head == null) return head;        ListNode A = head;        ListNode B = head.next;        while(B != null)        {            if(A.val != B.val)//比较时要用val, 记住！！A与B不同时            {                A.next = B;//确立好A的下一个是B的关系                A = A.next;//此时A也要往前走                B = B.next;//B也要往前走            }            else//A和B值相同            {                B = B.next; //B继续往下走，A继续原地等着                if(B == null) A.next=B;//如果B为空，说明是最后了，那A的next就为B，即空            }        }        return head;    }}