题解 | #删除有序链表中重复的元素-II#注意删除头节点的情况

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode deleteDuplicates (ListNode head) {
        // write code here
        if (head == null || head.next == null) {
            return head;
        }
        ListNode temp = head;
        ListNode lastNode = null;
        while (temp != null && temp.next != null) {
            boolean isNeedRemoveSelf = false;
            while (temp.next != null && temp.val == temp.next.val) {
                //重复删除
                isNeedRemoveSelf = true;
                temp.next = temp.next.next;
            }
            if (isNeedRemoveSelf) {
                if (lastNode == null) {
                    //删除头节点
                    head = head.next;
                    temp = head;
                } else {
                    lastNode.next = temp.next;
                    temp = temp.next;
                }
            } else {
                lastNode = temp;
                temp = temp.next;
            }
        }
        return head;
    }
}