public class TreeNode<K,V> {
    
    private K key;
    private V value;

    private TreeMap<K, V> tree;
    private TreeNode<K, V> sub;
    private TreeNode<K, V> top;

    public TreeNode(TreeMap<K, V> tree, K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() {
        return key;
    }

    public V getValue() {
        return value;
    }

    public V put(K key, V value) {
        int comparison = tree.getComparator().compare(this.key, key);

        if (comparison == -1) {
            if (sub == null) sub = new TreeNode<K,V>(tree, key, value);
            else sub.put(key, value);
            return null;
        } else if (comparison == 0) {
            V oldValue = this.value;
            this.value = value;
            return oldValue;
        } else {
            if (top == null) top = new TreeNode<K,V>(tree, key, value);
            else top.put(key, value);
            return null;
        }
    }

    public V get(K key) {
        int comparison = tree.getComparator().compare(this.key, key);

        if (comparison == -1) {
            if (sub == null) return null;
            else return sub.get(key);
        } else if (comparison == 0) {
            return value;
        } else {
            if (top == null) return null;
            else return top.get(key);
        }
    }

    public boolean containsKey(K key) {
        int comparison = tree.getComparator().compare(this.key, key);

        if (comparison == -1) {
            if (sub == null) return false;
            else return sub.containsKey(key);
        } else if (comparison == 0) {
            return true;
        } else {
            if (top == null) return false;
            else return top.containsKey(key);
        }
    }

    public TreeNode<K, V> getSub() {
        return sub;
    }

    public TreeNode<K, V> getTop() {
        return top;
    }

    public V remove(K key) {
        int comparison = tree.getComparator().compare(this.key, key);

        if (comparison == -1) {
            if (sub == null) return null;
            else {
                if (tree.getComparator().compare(key, sub.getKey()) == 0) {
                    V value = sub.getValue();
                    sub = null;

                    return value;
                } else {
                    return sub.remove(key);
                }
            }
        } else {
            if (top == null) return null;
            else {
                if (tree.getComparator().compare(key, top.getKey()) == 0) {
                    V value = top.getValue();
                    top = null;
                    return value;
                } else {
                    return top.remove(key);
                }
            }
        }
    }
}