83.remove duplicates from sorted list

/**
 * 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 p = head.next;
        ListNode result = head;
        ListNode tmp = head;
        while(p != null){
            if(tmp.val != p.val){
                tmp.next = p;
                tmp = tmp.next;
            }
            else {
            	tmp.next = null;
            }
            p = p.next;
        }
        return result;
    }
}

 while(p != null){
	if(tmp.val != p.val){
		tmp.next = p;
		tmp = tmp.next;
	}
	if(tmp.val == p.val) {
		tmp.next = null;
	}
	p = p.next;
}