Remove Duplicates from Sorted List II

描述
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.
分析
无

代码

public static ListNode deleteDuplicates2(ListNode head) {
        if (head == null || head.next == null) 
            return head;
        
        int t = Integer.MIN_VALUE;
        ListNode fakehead = new ListNode(t);// 加了个头指针
        fakehead.next = head;
        ListNode ptr0 = fakehead;
        ListNode ptr1 = fakehead.next;
        ListNode ptr2 = fakehead.next.next;
        boolean flag = false;
        while (ptr2 != null) {
            if (ptr1.data == ptr2.data) {
                flag = true;
                ptr2 = ptr2.next;
                ptr1 = ptr1.next;
                if (ptr2 == null)
                    ptr0.next = null;
            } else {
                if (flag) {
                    ptr0.next = ptr2;
                    flag = false;
                    ptr1 = ptr2;
                    ptr2 = ptr2.next;
                } else {
                    ptr0 = ptr0.next;
                    ptr1 = ptr2;
                    ptr2 = ptr2.next;
                }
            }
        }
        return fakehead.next;
    }