答案

/**
 * 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) {
        if(head==null||head.next==null)
        {
            return head;
        }
        ListNode first;
        ListNode next;
        for(first=head;first!=null;first=first.next)
        {
            next=first.next;
            while(next!=null)
            {
                if(next.val!=first.val)
                {
                    break;
                }
                next=next.next;
            }
            first.next=next;
        }
        return head;
    }
}