容易错的地方：要判断链表是否为空，为空直接返回

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head == null)return head;
        ListNode newNode = head;  
        while(newNode.next!=null){
            if(newNode.val == newNode.next.val){
                newNode.next = newNode.next.next;
            }else{
                newNode = newNode.next;
            }
        }
        return head;
    }
}