思路

1. 数组加哈希表
2. 数组存值
3. 哈希表筛选出不重复的值
4. 最后遍历筛选出来的值生成链表
5. 空间消耗大O(n),时间O(n)

unction deleteDuplicates( head ) {
    let arr = []
    while(head) {
        arr.push(head.val)
        head = head.next
    }
    let map = new Map()
    for(let item of arr) {
        map.set(item, (map.get(item) || 0 )+ 1)
    }
    let res = []
    for(let [index, item] of map.entries()) {
        if(item == 1) {
            res.push(index)
        }
    }
    let node = new ListNode(-1)
    let pre = node
    for(let item of res) {
        node.next = new ListNode(item)
        node = node.next
    }
    return pre.next
}