思路

快慢指针法

code

public ListNode deleteDuplicates(ListNode head) {
     //虚拟节点的next指向head 快指针指向head 慢指针指向dummy
     ListNode dummy = new ListNode(0),fast =head,slow = dummy;
     slow.next = fast;    //快慢指针连在一起
     while(fast!=null){   //一直到快指针到头
         while(fast.next!=null&&fast.val==fast.next.val){
             fast = fast.next;  //如果值重复 则将fast向后
         }
         if(slow.next!=fast){   //如果此时没有重复元素，则slow.next=fast
             slow.next = fast.next;  //将slow跳到fast
             fast = fast.next;      //将fast向后移动
         }else{
             slow = slow.next;   //如果没有则都相互移动
             fast = fast.next;
         }
     }
     return dummy.next;
}