java 代码

 class Solution {
    public ListNode deleteDuplication(ListNode head) {
        if (head == null) {
            return null;
        }

        ListNode list = head;
        int tmp = -1;
        ListNode pre = null;
        while(head.next!=null){
            ListNode frist = head;
            ListNode second = head.next;
            if(frist.val == second.val){//删除节点
                tmp = head.val;
                frist.val = second.val;
                frist.next = second.next;
            }else if(frist.val==tmp){
                frist.val = second.val;
                frist.next = second.next;
            }else{
                pre = head;//前一个节点
                head = head.next;//当前节点
            }
            if(head.next==null && head.val == tmp){//删除尾节点方法，是将倒数第二个节点的next设置为null
               if(pre!=null){
                   pre.next = null;
               }else{
                  return null; 
               }
            }
        }
        return list;
    }
}