LeetCode 82. 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.

链表去重问题，用三个指针和flag来判断是否指向了重复值

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head==null||head.next==null)return head;
        ListNode p = new ListNode(0);
        p.next = head;
        ListNode pre = p;
        ListNode cur = p.next;
        ListNode aft = p.next.next;
        boolean f = false;
        while(aft!=null){
            if(cur.val==aft.val){
                f = true;
                cur = aft;
                aft = aft.next;
                if(aft==null)pre.next = null;
            }
            else if(f){
                pre.next = aft;
                cur = aft;
                aft = aft.next;
                f = false;
            }
            else{
                pre.next = cur;
                pre = pre.next;
                cur = aft;
                aft = aft.next;               
            }
        }
        return p.next;

    }
}