题解 | #删除有序链表中重复的元素-II#

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;
        }
        Map<Integer, Integer> map = new HashMap<>();
        ListNode cur = head;
        while (cur != null) {
            map.put(cur.val, map.getOrDefault(cur.val, 0) + 1);
            cur = cur.next;
        }
        ListNode tail = new ListNode(0);
        ListNode newHead = null;
        cur = head;
        while (cur != null) {
            if (map.get(cur.val)  == 1) {
                if (newHead == null) {
                    newHead = cur;
                }
                tail.next = cur;
                tail = cur;
            }
            cur = cur.next;
        }
        tail.next = null;
        return newHead;
    }
}