/*
 * 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
        if(head == null || head.next == null){
            return head;
        }
        ListNode  currentNode = head;
        while(currentNode != null){
             ListNode next = currentNode.next;
              
                 if(next != null &&currentNode.val == next.val){
                     ListNode temp = next.next;
                     currentNode.next = temp;
                 }else{
                     
                     currentNode = next;
                 }
             
            
        }
        return head;
    }
}