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
        ListNode pre = null;
        ListNode newList = head;
        while(head != null){
            pre = head;
            head = head.next;
            while(head != null && pre.val == head.val){
                head = head.next;
                pre.next = head;
            }
        }
        return newList;
    }
}

②,pre和head 同步移动,如果pre和head值相同,head单独向前移动,并把pre的next指向最新的head

重复以上过程