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   class DummyClass {
        private class Node {
            int key;
            int value;
            Node pre;
            Node next;
            Node(int key, int value) {
                this.key = key;
                this.value = value;
            }
        }
        private Map<Integer, Node> map;
        private int capacity;
        private Node head;
        private Node tail;
        public DummyClass(int capacity) {
            this.map = new HashMap<>();
            this.capacity = capacity;
            this.head = new Node(0, 0);
            this.tail = new Node(0, 0);
            head.pre = null;
            head.next = tail;
            tail.pre = head;
            tail.next = null;
        }
        private void deleteNode(Node node) {
            node.pre.next = node.next;
            node.next.pre = node.pre;
        }
        private void insertToHead(Node node) {
            Node headNext = head.next;
            head.next = node;
            headNext.pre = node;
            node.pre = head;
            node.next = headNext;
        }
        public int get(int key) {
            if(!map.containsKey(key)) {
                return -1;
            }
            Node node = map.get(key);
            deleteNode(node);
            insertToHead(node);
            return node.value;
        }
        public void put(int key, int value) {
            if(!map.containsKey(key)) {
                if(map.size() == capacity) {
                    map.remove(tail.pre.key);
                    deleteNode(tail.pre);
                }
                Node currNode = new Node(key, value);
                map.put(key, currNode);
                insertToHead(currNode);
            }
            else {
                Node currNode = map.get(key);
                deleteNode(currNode);
                currNode.value = value;
                map.put(key, currNode);
                insertToHead(currNode);
            }
        }
    }