leetcode : Remove Duplicates from Sorted List[算法基本功]

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head == null || head.next == null) {
            return head;
        }
        
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        //head = dummy;
        
        while(head!= null && head.next!= null) {
            ListNode tmp = head;
            while(head != null && head.next!= null) {
                if(head.val == head.next.val) {
                    head = head.next;
                } else {
                    break;
                }
            }
            tmp.next = head.next;
            head = head.next;
        }
        return dummy.next;
    }
}