Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
       if(head==null || head.next==null) return head;
       ListNode curr=head;
       Map<Integer,Integer> map=new HashMap<Integer,Integer>();
       while(curr!=null){
           if(map.containsKey(curr.val)){
               map.put(curr.val,map.get(curr.val)+1);
           }
           else{
               map.put(curr.val,1);
           }
           curr=curr.next;
       }
       curr=head;
       ListNode prev=new ListNode(0);
       ListNode p=prev;
       prev.next=null;
       while(curr!=null){
           if(map.get(curr.val)<=1){
               prev.next=curr;
               curr=curr.next;
               prev=prev.next;
               prev.next=null;
           }
           else curr=curr.next;
       }
       return p.next;
    }
}