LeetCode 146: LRU Cache

class LRUCache {
    private int _capacity;
    private int _currentSize;
    private Map<Integer, Node> nodeMap;
    private Node head;
    private Node tail;
    class Node {
        public int key;
        public int value;
        public Node next;
        public Node prev;
        
        public Node(int k, int v) {
            key = k;
            value = v;
        }
    }

    public LRUCache(int capacity) {
        _capacity = capacity;
        _currentSize = 0;
        head = new Node(0, 0);
        tail = new Node(0, 0);
        tail.prev = head;
        head.next = tail;
        nodeMap = new HashMap<>();
    }
    
    public int get(int key) {
        if (!nodeMap.containsKey(key)) {
            return -1;
        }
        moveNode(nodeMap.get(key));
        return nodeMap.get(key).value;
    }
    
    public void put(int key, int value) {
        if (!nodeMap.containsKey(key)) {
            if (_currentSize == _capacity) {
                nodeMap.remove(tail.prev.key);
                tail = tail.prev;
                tail.next = null;
                _currentSize--;
            }
            Node current = new Node(key, value);
            current.next = head.next;
            current.next.prev = current;
            current.prev = head;
            head.next = current;
            nodeMap.put(key, current);
            _currentSize++;
        } else {
            moveNode(nodeMap.get(key));
            nodeMap.get(key).value = value;
        }
    }
    
    private void moveNode(Node current) {
        current.next.prev = current.prev;
        current.prev.next= current.next;
        current.next = head.next;
        head.next.prev = current;
        head.next = current;
        current.prev = head;
    }
}

/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache obj = new LRUCache(capacity);
 * int param_1 = obj.get(key);
 * obj.put(key,value);
 */