最基本的链表题目，需要注意的问题就是最后别忘了tail.next = null这样一回事…

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode tail = new ListNode();
        ListNode dummy = tail;
        while(head != null) {
            if(head.next == null || head.val != head.next.val) {
                tail.next = head;
                tail = tail.next;
            }
            while(head.next != null && head.val == head.next.val) {
                head = head.next;
            }
            head = head.next;
        }
        tail.next = null;
        return dummy.next;
    }
}