思路:

• 首要统计数组中每个元素出现的频次以及出现顺序(以第一次出现的为准)
• 创建一个结构体,包含: val count order
• 构造一个比较器确定比较规则(按照出现次数多少从大到小排序,出现次数相同则按照出现顺序order排序)

    public static int[] fx(int[] arr) {
        //收集节点信息
        HashMap<Integer, Node> map = new HashMap<>();
        int count = 0;
        for (int val : arr) {
            if (!map.containsKey(val)) {
                Node node = new Node(val, 1, count);
                map.put(val, node);
                count++;
            } else {
                Node node = map.get(val);
                node.count = node.count + 1;
                map.put(val, node);
            }
        }

        Collection<Node> values = map.values();
        Node[] nodes = values.toArray(new Node[0]);
        //生成信息后的原始节点信息
        for (Node n : nodes) {
            System.out.println(n.val + "\t" + n.count + "\t" + n.order);
        }

        System.out.println();

        Arrays.sort(nodes, new NodeComparator());
        //排序后的节点
        for (Node node : nodes) {
            System.out.println(node.val + "\t" + node.count + "\t" + node.order);
        }

        System.out.println();

        int[] res = new int[count];
        for (int i = 0; i < res.length; i++) {
            res[i] = nodes[i].val;
        }
        System.out.println(Arrays.toString(res));

        return res;
    }


    private static class Node {
        public int val; //值
        public int count; //值重复次数
        public int order; //顺序

        public Node(int val, int count, int order) {
            this.val = val;
            this.count = count;
            this.order = order;
        }
    }

    private static class NodeComparator implements Comparator<Node> {
        @Override
        public int compare(Node o1, Node o2) {
            //构建比较器,统计次不同时按次数比较否则按出现顺序排序
            return o1.count != o2.count ? o2.count - o1.count : o1.order - o2.order;
        }
    }