leetcode -- 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.

[解题思路]

在头结点之前添加safeguard，防止处理一开始就是连续节点的情况

当发现连续节点时，line 29删除重复节点，line 35-39处理剩余的一个重复节点

需要注意的一个test case：[1,1,2,2]，之前line 40-41 是在while语句之后，不能处理这种情况

现在当出现连续节点时，pre,cur指针不移动，继续检查删除后的情况

/**
 * 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) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(head == null){
            return head;
        }
        
        ListNode fake = new ListNode(Integer.MIN_VALUE);
        fake.next = head;
        head = fake;
        
        ListNode pre = head, cur = head.next;
        while(cur != null){
            boolean flag = false;
            while(cur != null && cur.next != null){
                if(cur.val == cur.next.val){
29                     cur.next = cur.next.next;
                    flag = true;
                } else {
                    break;
                }
            }
35             if(flag){
36                pre.next = cur.next; 
37                cur = pre.next;
38                continue;
39             }
            pre = cur;
            cur = cur.next;
        }
        return head.next;
    }
}