# 1836. Remove Duplicates From an Unsorted Linked List
###### tags: `Leetcode` `Medium` `Linked List`
Link: https://leetcode.com/problems/remove-duplicates-from-an-unsorted-linked-list/
## 思路
首先找到每个val出现的次数
然后遍历整个list如果当前node出现不止一次就要把当前node删掉
因为要删掉当前node 所以我们在回圈里面其实是看curr.next.val出现了几次
并且还要加一个dummynode来防止把head删掉
## Code

class Solution {
    public ListNode deleteDuplicatesUnsorted(ListNode head) {
        ListNode dummyNode = new ListNode(0);
        dummyNode.next = head;
        Map<Integer, Integer> cnt = new HashMap<>();
        ListNode curr = head;
        while(curr!=null){
            cnt.put(curr.val, cnt.getOrDefault(curr.val, 0)+1);
            curr = curr.next;
        }
        
        curr = dummyNode;
        while(curr!=null && curr.next!=null){
            if(cnt.get(curr.next.val)>1){
                curr.next = curr.next.next;
            }
            else{
                curr = curr.next;
            }
        }
        return dummyNode.next;
    }
}